This is the twilight part of a wedding the bride etc is off for photos and the rest of the guests are left to their own devices. You normally get the canapés and the standard issue of a half glass of “Bubbly”.
People mill around and then form groups of people who know each other and make idle chitchat. The bubbly usually runs out before the are bride and groom are finished ( Depends on timing), I think function
coordinators don’t want the guests to get to sloshed before the speeches start.