Very valuable depth. He can go back to the backline more permanently and shut down opposition small forwards. The team also has a few aging players in the backline who will be gone in a year or two at most.
As for playing up forward, Gia will probably miss a few games and there is no telling how Higgins will go with injuries. Same with Williams.
Will also depend on what happens if Wood gets traded.
Put it this way, Addison wouldn't exactly be demanding huge money, so having a player who is borderline best 22 (could be in or out depending on match ups), who is consistent, plays to the plan and can definitely hold his own at AFL level is better to have in the team than not.