I'm not really sure, but at this point in the season you will see some of it. A team might sign someone to a ten day contract to fill in a hole that they need filled until some player/s come back from injury, and while much of the time the player has no shot to earn a spot on the team, if they play well they might get picked up some other team. Much of the time this is used on players that have pretty much played their way out of the league and either has no chance to really play again in the league, or someone that if they play well could very well revive their career, but I wouldn't imagine it is clear to the player many times which one they happen to be, so it's not at all rare to see them play well in the hopes it gives them another shot. For example, Manny Harris was signed to two ten day contracts with the Lakers this year after they suffered from a horde of injuries and found themselves in need of some players to fill in some roster spots. He played well, and while he was not signed on again after his second contract was up earned himself some exposer with good performances, and at least from what I saw, showed he deserved to be on an NBA roster. How his performance when signed to those two ten day contracts plays out for him in future is unknown, but for now he is back to the D-League.