If the bride and groom have insisted on throwing the bouquet and the garter, and the guests have been polite enough to participate, the garter-catcher is expected to place it on the bouquet-catcher's leg and claim a dance. There's a certain pleasant symmetry to it. There's also the potential for trauma.
While the idea of bringing together a pair of sweethearts during this event is romantic, fate can have a wicked sense of humor. The situation is ripe for creepy mismatches. Cousins dancing with cousins. Old flames with enemies. Gawky 15-year olds gartering middle-aged aunts while the other guests laugh and clap. It's probably best to skip it and save everyone the nightmares later.
Wedding guest lists are getting smaller. But it's not just because weddings are getting more expensive. HowStuffWorks looks at the microwedding trend.