Of course this should be subjected to some rules; something like "play any move that's not bellow 0,70 the best move", or something similar.
My idea is to use such an engine in order to play some unorthodox openings without needing an opening book.
For example, say I want to play some games as White trying 1.e4 e4 2.a3. I'm sure there are many good moves for black's second move, so I'd like the engine to "choose" from several of them, instead of always playing the best one.
Kudos if this behavior could be limited to a fixed number of moves -so you get some variety in the opening but you want it "full power" on middle and endgame.