iOS 8 vs iOS 7 Group Messages
Group messages on iOS 7 are a pain. There is no way to leave one, and adding new people is a joke. In iOS 8 Apple solves most of the group message complaints iPhone users frequently share.
You can now name a group message so it is easier to make sure you get the right one. You can also add and remove people as you go, so you don't need to start a new Group Message.
Finally, and possibly most important. You can turn on Do Not Disturb for a single Group Message thread so you aren't getting alerts all the time. Then, jump in and see the conversation later when you have time.