I totally agree with Pull and MAB, belts have helped me realize form mistakes and helped correct them. Any bonus in extra weight used will be negated as I move forward. And like OR, I too only use them at 95% or above so that I'm using the knowledge/strength I gained on lower weights. Pretty soon, my belted max will be a nonbelted max, and so on.
Only other thing I will note that hasn't been discussed is that safety effect a belt gives you when you are maxing out. If you get forward on a max squat or deadlift without a belt, your lower back is in serious trouble. A belt can save you and allow you to train again a week later, as opposed to maybe months or years later if you eff up some disc or tiny ass muscle in your lower back.
I am Anton Zdravko Martin!
Best meet lifts: Sq 150 Kg (330 lb), Bench 120 Kg (264), DL 160 (352) @89 Kg (197)
Best gym lifts: Sq 375, Bench 280 (pause), DL 385 @205 or less
Goals beyond my wildest dreams, 600 Kg raw total, 200/160/240
Hack away at anything which isn't essential. Do what you love, and do it often. Fazc.
Everything competes for recovery so more assistance is not always the best idea. miked96