OMG they'z tota77y ROXXOR mang!!
Seriously, type like an intelligent person instead of a moron texting.
Yes, lots of people use them.
Benefits? explosiveness, power, fuctional strength. Will build your body as a whole unit instead of trying to split it by body parts.
They are the main core of my current routine. Snatch first, then clean and jerk, finish with snatch/clean pulls and squats.