I use it more to look for tendencies. Such as I have noticed we are typically a minus when marble is playing the pg. which doesn't mean he should never play pg but that we are using it for too long of stretches or putting the wrong guys around him when he is at pg.
think of it like this yesterday marble had 21 pts and 11 assts. but as I look at his game time I notice he had negative plus/minus values while playing pg. but this is while Jo was on the court and jo had a 17 pt game. Also the center during these times is typically olaseni who a lot of internet geniuses say is better than woody. That is telling to me.
i don't think it can be used just for individual players but it is interesting to look at for individual players. The key is to use it with groupings of players.