Have you ever been part of a group message that is annoyingly active? You want to see the conversation, but don't want the constant interruptions that can be a part of an active group.
In iOS 11, Apple made it much easier to hide the alerts for all messages, but more importantly group messages.
To hide alerts for messages:
1 - Open the messages App and find the conversation
2 - Swipe right to find the 'Hide Alerts' option, and select it.
You will now longer receive notifications about the message conversation, but can still view the message conversation.
3 - You'll see the 'Do Not Disturb' (moon icon) next to the conversation
4 - To activate alerts, swipe right and select 'Show Alerts'.