Recently I've been lifting heavier than usual, and I noticed:
1. My muscles actually seem to relax when I start lifting weights near my max, giving me better range of motion. I never get quite the same feeling from high-rep sets.
2. It's easier to stay focused when the reps are heavy. I don't lose concentration and lower the weight suddenly or perform a jerky movement.
I think that mindless reps are the ones the ones that hurt the most. Heavy or light isn't as important as the control you have over the weight.
Sure, you can go Ronnie style and lift too heavy, doing everything you can to grind out a weight you can't handle. But if you stay away from the extreme high-end, I think it's easier to control heavy weights. With light weights I always find myself being more careless, whether from fatigue, lack of attention, or something else.
I still like to do high volume, I just spread the reps out over more sets. That only leaves time for one or two main exercises, which is fine with me since I dont think variety really helps.