I know that I could continue without one and take care of my customers just fine. I'm 7 years into this job, and there have only been a few instances where I needed one. But... when I have an issue that is beyond my experience, I call one of my two senior techs and ask questions. They'll explain a concept, and I'll try to paint a mental picture of what is going on. All along, I'm wishing I could SEE the bus ripple, or the DV/DT reflections, or the harmonics, etc. I'm a very visual learner, and I can grasp a concept much faster if I can see what is happening. So part of this purchase is the education.
At first, I was trying to decide whether I needed a 4-channel, 190 series scope. I asked my senior tech what he thought, adding that I could buy either one. He said he's never had an instance where he needed more than his 2-channel Fluke 124. ...but he's very experienced, and "old school". That's not a bad thing, but I look at technology as a way to make the most of what I currently know.
I should add that my training is "Industrial Automation, Controls and Networking." My services go beyond VFDs for my smaller manufacturing customers. Most of the equipment I see is legacy. I'm always looking for a leg-up for troubleshooting. For instance, I've had an instance where seeing a Profibus signal quickly pointed to a physical issue in one of the many connectors. Like Bullzi said... when you need one, you really need one. The thing that caught my attention in the 125B is the communication "bus health" feature. It's mainly for legacy comms, but that's what I see.
And I should add... I remember Ken Roach discussing how he uses his 125B for comm troubleshooting. That's quite an endorsement right there.
I'm still open to hearing what others have to say, though. I don't like having regrets after spending that kind of money.