Often I find myself working on Levels with large, complex file structures. It can be quite annoying when Unreal opens up all my folders in the world outliner, maybe this is a feature that people enjoy but I know for me and others It can be quite annoying.
I believe a good method for closing all folders at once would be to alt + click on the small triangles located to the left of a folder name that is used to open/close individual folders in the world outliner. This method would allow the existing functionality to stay (the fact that the world outliner opens up all your folders) while expanding to accommodate other users needs, most people wouldn’t notice the change but the people who could benefit from this increased workflow would surely enjoy it.