you see thats the problem with bodybuilders. They go to get "in shape" or "get muscle". They have lost the real sense of weightlifting, which is to get stronger. Simply put, if you are lifting to get big or buffed or in shape, you aint lifting for real, and must as well go and play some chess whilst doing your barbell curls.
It is imperative to have a strong lower back, much more so than bulging biceps, for a fact, a strong core comes before bulging extremeties (or whatever is the latest bodybuilding fashioned bodypart), which means that a squat over 400 shouldnt be very difficult for a guy who has been lifting for a few years.
If you are not putting up a 400 plus squat or 500 plus deadlift, then the only time I see wearing a belt is for 1RM attempts, mainly because when you max out you stress the ligaments and tendons more than any other time. Other than tha, forget about the belt, plus 95% of the people that use it, do so to look powerful and impress people (they need a belt because they are going to lift such a huge weight they risk breaking their back) or because they simply are pussies who are scared to deadlift bodyweight.