Uhh. Collections are just that. Collections. It is bascially a bookmark folder in your account.
While you can organize with it anyway you like and the system allows, one suggested usage is "Add this game to a collection to save it for later"
You can brag with collections on your profile. Use them as reminders. Sort your favorites. Whatever.
This is why I made this thread: https://itch.io/t/3693485/do-not-update-your-games-by-deleting-them-and-uploadin...
It screws up collections if devs delete their page and remake it, even if the url stays the same. Games will dissappear silently this way. Out of sight, out of mind. The devs doing that are shooting in their own foot. Especially if the collection was named: "buy later"