When you add player folders into the game, you create a folder when the player joins, and delete it as the player is leaving the game. This is to remove the residue of a player folder behind and possibly cause issues.
If I wanted to add players to a collision group when they join, do I also have to remove them when they leave? Or will it automatically do this since the part(s) added to the collision group no longer exist in the game?
Yes, They’ll be garbage collected from memory, since CollisionGroups are builtin they won’t hold a reference and the items can be garbage collected.
When you :Destroy() something, you don’t actually remove everything. It just removes all references and connections to the object. This is then completely wiped from by lua’s builtin Garbage Collector later on by its own process.