Washout use to be built into about everything.  We've tended away from it. 

It works by preventing the tips from stalling before the rest of the wing.  Tip stalls are why old timers warn not to start with warbirds.  Some (real and model) had a very nasty tendency to stall violently - even at non-landing speeds when that wing began to stall from maneuvers.  Foamies tend to have some - possibly caused by the wing warping more the further it is from the fuselage.