Would a builder choose to hammer nails with his hand, or use a hammer?
Kind of a stupid analogy if you ask me, but it gets the point across.
Why limit yourself in lifting by choosing to go against a belt when lifting near-maximum weights?
What do belts actually do? And where do they become important in lifting?
Belt's provide a layer of support, the tension on generally weaker areas of the body;
The Lower back & Core. But the belt is much more important than that, it also prevents hyperextension in overhead lifts, and allows novice lifters to practice tensing their core before a lift, by using the belt as a guide to push against.
So when looking at lifting heavy on your next top set, max out day or lifting meet, add the belt.