A good gun belt is important for proper wear and performance of a holster. A gun belt is different from a standard dress belt. A real gun belt is going to be:
Designed to be rigid and strong in the areas necessary to properly support a holster and any accessories.
Thicker than a normal belt. This extra thickness equates to additional strength and support.
More durable that a standard belt. Most standard belts are made of a thinner leather. Over time and use, the thinner leather may break down. This break down causes the belt to stretch and sag.