Group messages are great when you want to talk to multiple people at the same time. However, things can get disorderly real fast in the Messages app, especially if the same person is in multiple group conversations. That's where custom group names come in, which helps you make sense of all those disorganized threads with multiple names/numbers attached.
If you've accidentally turned on "Read Receipts" for all of your iMessages, there's an easy way to disable it so that no one knows when you're actually reading their incoming messages. You could also pick and choose which conversations can see that you've read their messages if you don't want to kill the feature entirely.
With iOS 9.3.5, as well as all of the versions prior to that, you had two choices when it came to "Read Receipts" for iMessage — either on for everybody or off for everybody. So if you weren't comfortable with one or two of your contacts knowing whether or not you've read their messages, you had to keep the feature disabled and miss out on Read Receipts for people you're a bit closer to.