A parameter called on-resize( Command that is called when this control is resized ), given to window controls would be useful.
You could use this to say, let a player resize a window in height, but not in width. Also you could use it to update the position of transparent windows with labels using the same background color( thus making the labels transparent too ) and allowing something like a WoWesque chat output( demonstrated in byond://mikau.mik_chat ) much more efficiently.
Aside from these, I'm sure it could be put to other creative uses.
Yes, no, maybe?