Usually a form of GraphicalUserInterface.
PowerUsers and CompulsiveCustomizers love them.
MicrosoftOffice is a classic example with its toolbars. You can spend many happy hours dragging them around, making them into little windows and drawing new controls.
Someone (any idea who? is this just a vibe or was a Study done?) mentioned that some users can end up permanently losing a toolbar, because they tear it off and close the window. Then they don't know how to get it back.
Again I feel like mentioning PerpetualBeginners but I'm not convinced that it's polite to talk behind their backs like this.
Well, I've known a couple people who did just that, so certainly it happens. -- DanielKnapp
See also BlinkingTwelveProblem
FvWM (the window manager) and Emacs are also good examples of this driven to the extreme (not necessarily bad).