why in the world would the leafs take on a massive salary they dont need to to clear like 500k in cap space?

No, the Leafs don't get cap relief by having Kesler. Could you explain why? Kesler cap is just added and then taking subtracted. Now the Leafs save cap by trading Engvall, not by acquiring Kesler.

The Ducks don't need another bottom-6 lefty

If we want Engvall, we'll pick him up whenever he's put on waivers.

If the Leafs add Kessler, they can put him on LTIR which basically means that his cap hit gets added on top of the 81.5 salary cap and that’s how much more the Leafs can spend. They could use this to go after Tarasenko, but that’s just me dreaming. (And LTIR is a lot more complicated, but that’s basically the gist of it)

As much as Leafs fans bash Dubas, he’s not that stupid, he’s going to shop Engvall around before putting him on waivers to at least try to get something for him, so even if it’s not the Ducks, he could go somewhere else like Chicago and take back Shaw’s contract

Nice job being over the cap

I learned from Tampa Bay

The Leafs at at their cap limit of 81.5m with "active" players. Adding Kesler just adds 6m more...but then you subtract because of LTIR and it still leaves the Leafs at the 81.5m limit.
Adding Kesler and putting him LTIR does not allow the Leafs to add another big contract for 6m, for an active roster of 87.5m

You’re right, adding Kesler’s $6 mil does not mean that the Leafs get a special cap hit of $87.5 mil, it’s a lot more complicated than that. However, adding Kessler’s contract to LTIR does mean that they can exceed the cap and still remain cap compliant for the season. The Leafs have done it before using Joffery Lupul’s contract, Nathan Horton’s contract, David Clarkson’s contract, and Tampa Bay looks to do the same thing by getting Brent Seabrook’s contract from Chicago

No, the Leafs still were at the "active player" limit the cap hit at the time regardless of the LTIRs they had.
Having Horton did not have help the Leafs cap at all. Trading the 5.5m Clarkson to Columbus helped the Leafs cap because they could use that 5.5m more effectively. The only reason Columbus made the trade was because Horton's contract was uninsured, and they thought they could get value out of Clarkson, regardless of his inflated cap hit, instead of being out of pocket 27.5m for Horton's uninsured contract. Actually Horton's last year as Leafs he was IR not LTIR. Leafs would have a big bonus carryover the following year which they couldn't afford the following season. So in that season the Le afs actually had to stay 5.5m under the cap with active players.
Having Lupul on LTIR, helped the Leafs because they could replace his 5.25m cap hit with better value.
Tampa who are at the cap limit do not benefit by having Seabrook on LTIR. He was probably just part of the trade as the now Tampa has to pay his uninsured part of the contract. It certainly doesn't benefit Tampa cap wise.
Leafs are at the cap limit now...actually over it. Kesler makes no difference to the Leafs cap expenditures.

First, Horton was on LTIR the whole time his contract was with the Leafs, never IR (literally just google “Nathan Horton LTIR”) and Clarkson was traded back to the Leafs from Vegas just to be put on LTIR and allow the Leafs to be cap compliant with Marleau’s monster deal.
It makes no sense as to why Tampa would make that trade if it didn’t benefit them cap wise, giving up not only Tyler Johnson but a second round pick is a steep price to pay to gain absolutely nothing, especially since Seabrook’s contract has a higher aav than Johnson’s.

Bonus point, it was suggested that the Leafs get Kesler at the beginning of last season to be used as LTIR relief. So I doubt that would have been suggested if he didn’t make a difference in the Leafs cap situation.
(Incase you want to read up on that)

Thanks for proving my point.
Sorry, Horton was IR in his last season because it would have affected the huge Leafs bonuses.
Gaborik was traded to the Tampa....not because it helped Tampas cap, but because Gaborik's contract was only 80% insured. Melnyk saved about 600,000 in cash, but it didn't help the Tampas cap.
Johnson was put on waivers for and had no takers due to the fact he isn't worth his 5m. X 3 contract. Chicago agreed to take him, and they got a second round sweetener. Again LTIR Seabrook doesn't help or hurt Tampa's cap. Getting rid of the non productive at 5m Johnson was to Tampa's benefit. Looks like Seabrook was added to the trade so the Hawks would save actual $$$$ due to his contract not being fully insured. That $$$$ saving will be used probably to offset the $$$$ buyout when likely Johnson is bought out at some time.
Clarkson's trade back to the Leafs from Vegas was a quirk in the LTIR. The only reason the Leafs did it was because Marner was possibly not going to signed before the season started. Marner's cap was going to higher than his actual contract the fewer games he played. When Marner signed before the season started, Clarkson's LTIR meant nothing to the Leafs cap.