In the winter months when the gym is cold.. I would imagine "jump-squats" for a warmup could be a real bitch on the knees.
I would just warm up with bodyweight squats or just an empty bar. Follow the motion that you would be using for back squats.
Seems there's some kind of new hype goin on in the gym these days with all the unilateral, jumping, balancing, non-heavy-lifting. I guess they call it functional training. I see guys with the stretch bands doing the suspended cross-chest flyes in the squat rack. They are just inches from knocking their teeth out.
Add a Bosu ball and youve got a complete disaster.