Belts are very useful when you reach heavier weights, but the biggest mistake that everyone makes about a lifter's belt is in thinking that they are for back support. You can destroy your back just as easily without a belt as you can with one. (Speaking from experience there.)

All a belt does is give your abdomen something to push against when you need the support. It doesn't do anything to compensate for bad form.

I don't know about belts, though. I think if you're lifting with appropriate form and not attempting weight for which you're not ready, you shouldn't need one at all, I've always felt they were a false-confidence thing, but YMMV. They don't appear to hurt when used properly, so I suppose it's a matter of preference.