it also works well for training, if you have a guard that you want to teach big man skills to, but dont want to switch him and your center's up, you can make your guard play offense as a center, and defend at the guard positions, while your Center will defend at the center position but play ofense at the guard positions. everyone gets the minutes, and you may nbot lode the game that way.
As far as defensive rebounding goes, i think that if your SG is guarding the opponents C, and your SG has lower rebounding you will be outrebounded at that position.