He’s not technically retiring, because that would forfeit the $16M remaining on his contract. The announcement is that he is unable to resume his playing career due to injury. This is an acknowledgement that Logan won’t ever again be medically cleared to play
The team cannot force him to retire. Nor can they waive him, reassign him to the AHL, trade, or buyout his contract—without his permission—since he’s injured.
He’ll be on IR for the next two years and will count on the cap; helping hit the cap floor if that’s what Grier needs. At the same time, should Grier want to use Logan’s $8M in cap space to sign some player, Couture can be moved to LTIR and the Sharks will be able to exceed the cap by up to $8M (including Couture’s salary). Functionally, Couture’s contract will in no way hinder whatever the Sharks want to do*
*Technically if Grier wants to spend to the cap at the very start of either of the next two seasons, like the literal first day of the league calendar start, he’d have to do some paper shenanigans to fit Couture’s contract under the cap prior to placing him on LTIR for the season.