My husband and I play unrated games with the goal being to stay connected throughout our work day. He lets me win about half of our games, or more, otherwise I would probably call it quits. In his games with me, he has to figure out how hard he can play without me having to call him at work to remind him of the rules (we've settled on the rule that his queen can't move, and sometimes he has to not take, he just gets to rub it in that he could take it if he wanted). Very, very hard, for both of us. Last night he took my queen right before we went to bed. Lets just say he didn't sleep so well ;-)
Surprisingly, it has made me a better player and I have thrown moves/games if I feel someone's moral is suffering - everyone needs a break now and then.
I have done it while teaching a kid how to play and I try to do it so I can get my girlfriend to play...
But I don't think that counts at all