I may be on the wrong track here, but I'll give it a go. They were probably thinking that the inertial load of the drill is not enough to worry about. The more rotating mass/inertial load of the system(loaded belt conveyors, revolving mills) , the more significant the regeneration. If you can deal with a longer decelleration time, then the surge is manageable, but if you actually use the drive to control the slow down, then you'll see more current and need somewhere to send it, so it gets directed to the resistors to be converted into heat.
The really high end models are true regenerative models that actually convert the braking energy back into A/C and return it to your process.
Anyhow, good luck with the purchase and installation, we'll be glad to hear how the combination of parts work out for your purpose.
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