Apparently, "cheesing it" is a gaming slang for cheating in a game to get through a boss encounter or difficult battle, though I think a more appropriate meaning would be exploiting a games mechanics, AI, or environment to defeat that boss (or any difficult battle).
One could as well say, there's a reason it's called cheesing, and NOT cheating. Let the idiots that aren't observant or intelligent enough to notice AI weaknesses that can be exploited think it's cheating. They're really just overcompensating for not being smart enough to figure the game out.
I really only use cheesing if the developer makes certain bosses really bullet spongy, which I'm OK with in a shooter game, but in a survival horror game where resources are limited, not so much. I'm also OK with it if the boss takes time to kill due to needing to go through several phases with the help of a squad, like the battle against the Swarmak in GoW 4. This can be a tough fight on Insane difficulty, but when you consider your squad mates can revive one another, there are ample ammo caches, and the fight can be done without shooting all blisters, it's perfectly fine for it to be hard. Shooting all blisters really only makes it even harder since you have to take fire getting to certain vantage points, and each blister popped takes you to another phase that adds ground troops. The alternative way is to stay at a distance in the center and blast the hell out of it's belly for several minutes. You won't get the checkpoints this way, but it's a lot less to manage. This method isn't so much a cheese as an alternative tactic.
There are bosses in some games I have no problem cheesing though, like the Waterwheel boss in RE Village, and Moreau in the same game. The Waterwheel boss can be cheesed by luring him (by shooting at him) to the rooftop of the house near where he attacks you, then positioning yourself on the edge of the roof on the far side of the chimney from where you climb the ladder. This makes him stay on the roof edge on the other side of the chimney, without enough roof between the chimney and roof's edge for him to cross over to you. He'll just keep swatting at you a couple times then fall to his face, at which point he's still and open for headshots. I once had him climb up the roof and come around to my side though, so it's not a 100% cheese.
The Moreau boss fight in the drained swamp on Village of Shadows difficulty can take 40 minutes or more by conventional means, even if you shoot all the explosive barrels when he's near them. There's a simple trick to lure him into getting stuck on the corner of those buildings that have a sort of corner porch, with a supporting post at the very corner of the roof. He gets wedged into that spot and can't get free, whereby it's easier to get in close shots at Moreau when the beast opens it's mouth. You're still going to drain a ton of your ammo even with this cheese though, and it takes at least 13-14 min.