because in order to get the full benefit of LTIR the team has to remain right around the upper limit salary cap. Currently Tampa has $6,880,456M in cap space and with you keeping Callahan they would only be allowed to go over the cap by $2,778,331M .. so moving him actually gives them more cap space

I thought I read that during the year you can go over the cap but it has an adverse effect on next year. Tried but can’t confirm. Do you know? Ottawa did the deal because cally on ir is an insurance case so actual pay out very little s as nd the goalie we toke actual salary hire than the cap hit. Difference between Vinik and the Ottawa owner.

No teams cannot go over the cap during the year, only in the playoffs. However as the season progresses a players contract becomes more and more prorated so a team pseudo accrues cap space depending on how far below the cap they are. If a team puts a player on LTIR to stay below the cap they can only go above the cap by the sum total of their current cap hit + the LTIR contract(s).
In Tampa's position, if they put Cally ob LTIR they would barely be over the cap if his contract was included so incase of injuries during the season they were nuch better off moving him and staying just below the cap.
For Vegas, there is a difference between your regular LTIR pool and bonus LTIR pool so by moving Clarkson they avoided a recapture fee on next years cap.
For Toronto by trading for Clarkson it allowed them to have protection incase of a Marner offersheet as well as put them super close to the cap ceiling putting him and Horton on LTIR

The only way a team can go "over" the cap for the season is by bonus payouts at the end of the season. If a team has enough cap space to cover the bonus' they're fine, but if they don't there'd considered "overages" and get applied to the next seasons cap