A lot of directors don't know what they want to do. Every director I've seen that was a good director that I've admired knew exactly what he wanted to do. They didn't sit there and think about it.
There are definitely reasons to do certain things, but I like to stick to good director, good actor, good script.
I think what makes a good actor's director is the same thing that makes a good director. Acting is just one of the trades necessary to make a movie.