Ok, time to expand on milldrone's response by mixing DickDVs in with a smattering of specifics to the PF70. It's a long one, but I have the time since I'm at home recuperating after surgery.
In milldrone's response, I think he nailed it as to the possible reason why someone would install a DB resistor and yet not use the DB function. In fact that is a highly likely reason. However, we don't know for sure, because we can't read the mind of the original designer, nor can we see the application. So unless you know FOR SURE that something is wrong, I suggest not messing with it. Now the details.
As DickDV said, there are different modes of electronically braking a load once you have a VFD (although these can also be stand-alone devices, they are typically built-in to most VFDs); Dynamic Braking or DB, and DC Injection Braking or DCIB. But first lets establish that when braking any moving load there is kinetic energy in that load, so because energy cannot be created or destroyed, only transferred, braking involves converting (transmuting) that kinetic energy into some more controllable form. if you have a mechanical braking system, such as on a car, that kinetic energy is transmuted into friction and the heat it creates, and of course wears out the brakes. Electronic braking is the alternative. My wife has a Gen 1 Prius with 280,000 miles on it, we have never had a brake job done yet. That's why industry likes to use electronic braking if they can, and when you already have a VFD, you have it.
With DB, the motor is turned into an induction generator, then the kinetic energy in the load is transmuted into electrical energy and dumped off somewhere. That "somewhere" can be resistors, which transmute it again into heat outside of the system where it is safely radiated, or in the case of a "regenerative" drive, used to power other drives or loads. But to start with, turning an induction motor into an induction generator means you have some specific issues to deal with. For a motor to be a generator, it must have power applied to it, because there are no permanent magnets, they are all electromagnets, this is referred to as "excitation energy". The other necessary component is that the rotor of the generator must be turning faster than the relative rotational frequency of the stator, referred to as "over hauling". So using the frequency control capabilities of the VFD, the stator remains energized so that the motor receives excitation, then the frequency is ramped down in such a way as to ALWAYS be lower than the rotational speed of the rotor, which is connected to the load, so the load is always kept in an over hauling state. The VFD doesn't necessarilly need to actually know the speed of the load, it just watches the DC bus voltage and if it begins to drop, it lowers the stator frequency more and more to keep the energy flow going back INTO the drive. So of you notice my highlight, this can ONLY be accomplished by having the VFD in "ramp mode" for stopping. The other choices involve REMOVING power from the output (coasting), or applying DC only from it, our next form of braking. Neither of those will turn the motor into a generator. The advantage of DB is on being able to very quickly move that kinetic energy out of the motor and load, and put it somewhere else safely. The disadvantage is that it suffers from the law of diminishing returns; the slower the load gets, the less energy remains and the less braking power you have. In fact, a DB braking system alone can never "finish the job" of coming to a complete stop. In the end, it either ends up coasting, or you need some other form of braking. If you have mechanical brakes, you engage them, and because most of the kinetic energy is already gone, they get very little wear. That's what the Prius does. But if you DON'T have a mechanical brake, enter DCIB.
With DCIB, the output of the VFD is changed to be DC only, applied to two poles. This creates a stationary magnetic field in the stator. As the rotor passes through it, it still has its fields induced, but now they are going to be counter rotating to the direction of the load. That will pull the rotor into a stationary position in line with the stator DC field and the load stops. The advantage to this is that it can finish the job, bring it to a complete stop and even hold it there temporarily. The disadvantage is, all that kinetic energy is trapped as heat INSIDE OF THE MOTOR. So DCIB has a relatively severely limited duty cycle in that every braking operation looks the same, thermally, as a starting cycle as far as the motor thermal damage curve is concerned. So the rule of thumb is, when using DCIB, cut the motor Starts-Per-Hour rating in half. For small motors rated at 20 Starts-Per-Hour, might not be a problem but for large motors that might be rated for 2 Starts-Per-Hour, you can be forced to wait up to an hour before restarting it depending on when it was started and braked. In addition, full braking torque requires full current, including what would have been STARTING current had the motor been started Across-The-Line, and unless the VFD is over sized by about 4X, it's not likely to be able to deliver that. So instead, the VFD provides a lower level of DC current, what the transistors can safely handle, which translates to longer stopping times.
So the "perfect" combination to stopping a load with a VFD is to remove MOST of the kinetic energy with DB and put it somewhere else, then FINISH the job with DCIB once you lose the effectiveness of the DB action. For THAT reason, DCIB is usually programmed to engage at a programmable trigger speed, i.e. the final 10-30% of rotational speed after DB is through with it. Using this, there is usually no reason to need to select DCIB with an input, because once enabled, you must then also program the trigger speed and current values you want, which makes it automatic. But remember, the VFD is not capable of more continuous current than the power devices are rated for. So if for example you set the trigger speed for 100% of the max speed, the instant you hit the stop button, the VFD is braking the load. But if you have the DCIB current set for 300%, the drive can only deliver that for a second or so, and will disengage the DCIB to protect itself. If you set the current limit to 100% it can do that all day, but your load may take a long time to stop. If you are using DB first, the Stop mode is set to Ramp, which keeps the motor powered, you set the Decel ramp for the stop time you want, and again within the limits of the VFD components, it pumps the energy off into the resistors and when it gets to the trigger speed of the DCIB, the ramp is turned off and the DC is injected, finishing the job.
Now the specifics of the PF70 as it relates to milldrone's theory. The PF70 has a feature called DC Bus Regulation in which it will attempt to deal with excess DC bus voltage in the way you program it to. The excess bus voltage can come from line voltage swings, but also from the load, most famously from eccentric loads like pump jacks and vibrating machines, where an eccentric weight requires motoring as the weight is lifted, then as it falls, the motor regenerates. So this is DIFFERENT from braking in that it is for use when RUNNING, not stopping, but the same issues remain; what to do with the energy. One option on DC Bus Reg is to have the drive modulate the frequency to prevent it from happening; don't allow the motor to become a generator by not allowing negative slip. But that is difficult to implement with constantly changing loads and can't help with line voltage surges anyway. So the other option is to dump into the resistors as needed WHILE RUNNING, not just when braking. THAT is what your programming is indicating was the choice here. Most likely the load did NOT need Dynamic Braking because coasting o a stop might happen quickly anyway, but the still wanted to ensure it completely stops, so the DCIB is triggered at some low speed. But for other reasons, they have the DC Bus Reg programmed to utilize the resistors as a means to dissipate any excess DC bus voltage.
So again, unless you can get into the mind of whomever made these decisions, I suggest not messing with anything that has been working fine for years. Now hopefully you know why.