With Stassi and Fletcher, the Braves took on an extra $6 million. They could pay $4 million of Stassi's contract if they found a taker for the remaining $3 million. That in effect lowers the cost for Fletcher to $3 million, and if they get a player back for Stassi at that point, then that player is added onto Fletcher as the return for that $3 million.
TB is looking for catching, so I could see Stassi as part of a Glasnow deal, but the Barves will have to eat even more of Stassi's contract. Perhaps they go after Margot, too, for OF depth.