We are not paying to trade Bouwmeester. Jay Bouwmeester was hurt almost the entire time he played last season. If he is useless this season, we still do not need the cap room, nor do we necessarily need a replacement for him.
As for OP this does absolutely nothing for St. Louis and heavily favors MTL in value. Bouwmeester may not be worth a lot at this point in his career but I can guarantee you someone who needs a left handed stay at home defensemen and wants to take a chance on his mobility someone will offer a 3rd or 4th.