My understanding is that this paradigm was incredibly dangerous, with a lot of workers losing hands and arms in accidents. Turning on or off a given machine involved physically putting the belt on or pulling it off, and you could easily get caught in it. A very clever system for the technology of the day, but it's good we don't use it anymore, at least without more advanced safety mechanisms and practices.

I would have assumed they would have clutches so that individual machines could be disengaged. The large open belts running up to the drive shaft on the ceiling were dangerous regardless.