If your taken it up to your limits a couple of times a
month you won't be trainging the dead w/ out a belt for
ong.
Keep in mind even with a belt you are still training
your lower back and mid section but once you get past 300lbs. and work your way to 415 plus you increase your chances of working around a possible injury for the rest of your lifting days.
IMO its not worth it. I have had a minor back injury before and believe me they're no fun at all.
Not to mention it set me back months, and psychologicaly scarred me. By forcing me to understand yes I have a threshold and I have exceeded it.
Take it from me ignorance is bliss, wear a belt anytime your squating or dead lifting more than your body weight.
The purpose of a belt is to force you to maintain proper form. So you can do the excercise correctly and with less possibility for injury. Buy a good competition style belt. I have a Cardillo and I swear buy it. After I ordered a good belt my squat sky rocketed I went up a hundered pounds in just a few months, and my legs were almost the same size as my waist!!!
Its simple a belt allows you to focus on the parts your working. Also to keep you from swaying back and forth like a sapling in a strong wind while your trying to make the make the squat of your life.
http://www.cardillousa.com/belts/index.htm
This is the kind I have 450GL stock/black expensive but well worth it.