There's two reasons for making a deal at the deadline, or around it:
1. You're in contention, and you need to add a player.
2. You're out of contention, and you need to add prospects.
The reasoning is simple: Are you looking for short-term or long-term gain? That is, do you need one more piece to put together a contending team (and hence are willing to sacrifice the future to get it), or are you looking to build for the future? You might take a few chances on some marginal guys if you're in contention, the way the Yanks did on signing Sidney Ponson or Richie Sexson. Otherwise you either stand pat or collect prospects from the guys who are itching for that last piece.
