On the Golden Knight Vegas we see:

PROJECTED CAP HIT Tooltip : $84,174,999
PROJECTED LTIR USED Tooltip : $2,674,999
PROJECTED CAP SPACE Tooltip : $0 ($0 Tooltip)

Why is there "Projected LTIR used when David Clarkson is marked as an "IR" for the off-season, in place should it be account on the 10% allowed for the off-season cap hit ?

We project for the season, they are above the upper limit right now and unless there are roster adjustments the only way that is possible is through the use of ltir

Very clear thank you.

If thing were staying like that (big IF) what will be the effect on their cap hit at the trade deadline ? Can they accumulate more cap relief if say another player go on IR or LTIR ?

In Vegas's situation they can put Clarkson on LTIR any time. The only real benefit to having a player on IR, is if they under the cap with him on IR, they can pay their performance bonuses in that season instead of delay them. Vegas will not have a cap choice, Clarkson will be LTIR and teh 2019/20 bonuses (not that much) will have to carried over to 2020/21. So TDL isn't really a factor. And yes, teams can put any number of players on IR or LTIR at any time for cap relief.....well it has to be legit wilh league approval. Teams are not "cap punished" for having injured players.

Cap is kinda weird Kings didn't have enough to field a full team playing a guy short w/ only 500 short... They couldn't call up minimum salary player or something really stupid too... So played a game w/ a player down, like 11 forwards or 5 D-men instead of 12/6 or 18 skaters... So the cap sorta fluxes during season to give space... If click on teams on here... During season or near the deadline will see like "Deadline Cap" or something like that... So teams have room to make moves for cap deadline/deals its sorta weird... LTIR means doctor says player can't play for 10 games or 24 days... Once sees doctor that will come off the cap for most part depending how close they are to upper limit dictates how much space they get from it... Problem is they can't sign or make offers really until season starts to clear that money. So a few guys I think are still unsigned or RFAS they can't even tender in certain cases. Also they are retaining 500K from TAtar on their cap so only have 81M not 81.5 to start with .

OK so if I understand well the main factor to consider when you put a player on LTIR is team "performance bonuses" else to pay his salary (or if insured, part of it) and when to put him on LTIR if you want an ACSL as high as possible ?

The main reason to put a player on LTIR is to get cap relief so you can sign an similar priced player and keep your team as strong as it was.....again. "teams aren't cap punished for having LTIR players". The theme with 99% of Clarkson trades is that you are doing Vegas a big favour. There is no benefit or disadvantage to Vegas if Clarkson stay to Vegas. Leafs put Horton on IR last season, not LTIR because the Leafs did not want to have cap carryover into the very expensive 2019/20 season. But that was a very unusual circumstance as the Leafs had high performance bonuses due to their ELC status.