I would say the buttons to hide all the modules in the homepage.
I never need to see the online list, so I would love to be able to hide it.
Also, the "latest images in the gallery" panel in the homepage. I would love to be able to disable it, because I hate having useless things occupying space.
Obviously I'm talking from the point of view of an user, non of an admin, otherwise I would do these edits by myself... :D