When someone's ready to go, you can drag their speaker back to the drawer and it's instantly out of your party and ready for something else. Or you can go old school and just turn the speaker off. It's up to you.
Most parties get a little sticky - sometimes it can be a good thing. If you want to create a party that goes everywhere with you and is easy to crank back up the next hazy morning, go to the app's Settings and find the PartyUp settings. Just turn Sticky PartyUp on and turn up each time all of your speakers are powered on.
You can Party Up with UE BOOM, UE BOOM 2, and UE MEGABOOM. Just make sure each speaker is updated to the latest & greatest firmware, otherwise they won't be able to join the party and, really, no one wants to be left out.