The strongest argument is stability. The trousers do not wander, the crease stays in the middle of the leg and the shirt is less likely to come untucked. At a wedding you spend hours eating, sitting, standing and dancing, and the waistband neither presses nor needs adjusting. In those conditions a belt forces a compromise: it either feels comfortable or holds the trousers perfectly.
Braces work well with trousers worn higher, at the natural waist, and with pleated trousers. The trousers then fall straight, your legs look longer, and no shirt shows between the jacket button and the waistband.
Before you choose braces, check how they fasten. Classic braces attach to buttons sewn inside the waistband; if your trousers do not have them, a tailor can add them. Clip-on braces are quicker to put on, but they hold less securely, can slip off the cloth and look less refined, so for a suit choose the button-on kind. You can also wear braces with trousers that have belt loops: the loops simply stay empty.