I like the deal for Tampa because of one main reason, versatility. Since Gagner can play wing or center, and there seems to be conflicting comments on this thread about his effectiveness at either position, but he can do both if needed. I wonder if its a move to slot him as the #3 center with Kucherov/Connolly/Panik/Killorn/whoever so Johnson or Stammer can move to full time wing on the top line and the other stick to center. Johnson is better than a 3rd line center at this point and they really need him with top end players most nights.
If its not for Gagner to play center permanently, its always nice to have a guy who can do it if need be. Say Stamkos/Flip/Johnson gets hurt, Gagner slotter there is better than a rookie Drouin of Thomer having to play 3rd line minutes, like he did a lot last season. Its all about depth and options IMO