Some exercises lend themselves better to a full range of motion than others in my book. Squats for example I do a full range of motion, as well as all bicep and back work - anything that involves a squeeze and a stretch at either end of the rep.
However, there are some exercises that lend themselves to doing a rep range where as long as you go past the weakest point and then raise the weight, you wil get the benefit. I have proven this on myself - my strongest bodyparts in terms of size and strength are shoulders, chest, and triceps, yet I probably don't do a completely full range of motion on any of them, not the compound movements anyway. The smaller isolation exercises yes, but not the big mass building exercises - the muscle will still get worked effectively enough.