I'm generally of the opinion that one should choose either squats OR deadlifts, as doing both when you're training hard just ends up being too much--at least in my case. Since I've got my routine split up into a leg day, back day, and chest day I also try to focus on the particular muscle I'm working and give everything else a rest. Regular deadlifts are a whole-body lift, rack deadlifts tend to use a bit of leg strength, but mostly emphasize the back, traps, etc. When I do rack deadlifts I start the movement at about 1-2 inches above my knees. Plus, yes, I get to go heavier--though I've dropped the weight and focused on my form, since I got a bit carried away in trying to up my poundages, and my low-back was not happy. Feels much better now.