There's a now-discontinued addon called Kong Automatic UI Hider that would let you hide elements of UI and show them again upon mouseover/combat etc. If you have actionbars filled with inessential abilities that you don't always need to see the cooldown/availability of this can be useful, especially if your goal is to have a minimalistic UI. I tried some of the earlier versions on Wowinterface but they start at TBC and none seem to work for 1.12.
http://www.wowinterface.com/downloads/i ... Hider.html
Is anyone aware of an addon with similar functionality for 1.12, is interested in modifying the existing addon to work for 1.12, or creating a new addon altogether? I'm sure I'm not the only one who would like an addon like this.