Notifications can be useful when you want them, but you probably don’t care that much about getting a notification in every server you’re in. Especially servers with a lot of channels, and a lot of members talking all the time.
To Mute a server, just right-click on the server icon and check the Mute Server button. Easy! This will prevent notifications coming up for every message sent in the server. But you will still get notifications every time someone tags you or uses an @everyone tag. To remove that, right-click on the server icon, click on Notification Settings, and select to Supress @everyone and @here. Now the server is fully muted. If you do get tagged, you will still see the red notification dot on the server, but you will not get any sort of pop-up or audio alert.
If you want to see notifications from some channels but not others in a server, you can change that too. In the Notification Settings menu, you can select a channel and create custom notification rules for it. This may be useful if you’re in a server that talks about different games, but you personally only care about one or two of those games. In this case, you could mute the whole server, except for the channels dedicated to the games you like.