I tend to mix it up and have: proper form, explosive moves and slightly less than proper form...but they all depend on the exercise in question.
I will never consider less than proper form on exercises such as deadlifts, squats, RHDLs etc. RHDLs are probably the sole move that I'm in minute awareness of exactly what is occuring in my back even above and beyond the awareness I give to deadlifts and squats, due to the inherent dangers of the exercise.
Explosive moves are used where it's safe and sensible to do so.
Slightly less than proper form, but never way-off form, may be used for the latter reps in a bicep curl etc.