Dragging the sled has DRAMATICALLY increased my work capacity for deadlifting and squatting. Its great for the upper back as well, the latest thing I have been doing is pulling it with a neck harness GM style. I grew curious after seeing some of the guys at WSBB do it and it hits your whole body. Really good for "pumping" up the legs, hamstrings,hips,glutes,etc. There should be no debate on the benefits of doing it. Louie Simmons has written some articles about this on WSBB's homepage.