When I was younger I thought it was necessary to have a belt for most lifts, excluding bench presses. Like Longdog said, it keeps your stabilizers from developing. I've had lower back problems from an incident at work years ago. Because of this, I do wear a belt when going heavy on squats, deadlifts, and military presses. I found by not wearing a belt on all other lifts has helped me a great deal, and I have not had a problem with my back now for over 5 years. It has also helped with the development of my abs.