What was vomitorium used for?

Vomitorias are believed to be places, where Romans were vomiting during parties so that they were able to continue feasting. It's not true.

In fact Vomitorium was an exit in amphitheatres, stadiums or hippodromes, which allowed big crowds to exit after the games/play has ended. Vomitorias are still present in modern buildings.
The name Vomitorium comes from Latin word vomō, which means "to spew forth".