Main contactor in front of Sinamics infeed module S120

So far I have always seen a main contactor in front of a Sinamics infeed module of S120. Is this really necessary, since safety category 3 can be accomplished with the integrated safety of the drives. If it should be realy necessary, when should you start then the infeed module (and activate the main contactor) : all the time (f.i. when 24V is active in the cabinet, or when the plc is in run) or should you only activate the infeed if the drives have to be activated and shut down the infeed if the drives are not activated anymore.
Thanks

i have no experience with sinamics, but with masterdrives. but i learned that it is better to use a contactor to supply any drive. you cannot always trust the electronics to cut power off in case of a problem. this contactor should be always active except for the following two cases: either the drive has generated a fault and can no longer control the motor. or the emergency safety relay delayed output is off (you should use one with this feature).