If you have to hump up a bit to force a few more reps out of your muscles its ok. But yeah, this is basically all cross fitters do. they are also a bunch of cunts to others in the gym generally.
Basically, it's the idea that if you have **** form while exercising and do it for too long, you'll either get ripped faster, due to all the exertion or get seriously injured. More often than not, it's the latter.