There's been quite a controversy about the belt, I feel. Some people love it and applaud it, others think there's no point to it.
The main question to ask, I think, is whether you are a pro or a beginner.
If you are just starting out, you don't really need a belt - you need to know precisely how to perform each lift, and having additional support might only hinder your progress.
On the other hand, if you have already reached your 85% of 1 RMP, you might want to look into a lifting belt. Research has shown that wearing belts raises the intra-muscular pressure of the erector spine muscles - in other words, you will be less likely to injure yourself when lifting more.
I've been using one in my gym sessions for a couple of years, and have come to realize I rely on it more and more. It provides adequate support to my lower back, and it gives me the added security to try and lift heavier.
In fact, I've come to learn that they have been around for nearly two centuries, and that the first lifting belts have been used around 1820, by the very first strongmen and have later gone on to be a reliable tool for Olympic lifters alike - which certainly means they will help you in both terms of stability and injury-prevention.