You cant put anyone on LTIR until the season starts. During the offseason, the hit counts against the cap. You can exceed the cap in the offseason, but not by much. Getting Savard's hit off the books allowed Boston to sign Beleskey as well as keep the rest of their RFAs. Savard's hit would have prevented them from making these moves.
Florida now has the option of putting him on LTIR or keeping him on the books during the season if they need to reach the cap floor.