Allowing people to group servers they are in into folders or hide them entirely would be super convenient for people close to the 100 server limit on Discord.

Examples:
1. You are in a bunch of servers only for emotes to use in Nitro so you never look at the actual server itself, hiding them de-clutters the list so it's easier to get to the servers you actually use.
2. Categorizing by topic so you can more easily find something (all your gaming servers in one folder, personal servers for friends in another, support servers for websites/bots in another, etc.)
3. Using it to make a priority system for productivity (like you have 5 folders and the highest folder is ones you know you need to respond/look at immediately when they get a reply while the lowest is ones you only need to check once a day or so)

You can technically do something similar already with Bookmarks but you can only bookmark individual channels, not full servers, and it doesn't hide the item in the full server list (this would only show the server in said group so no duplication)