"Cheese" is a term that's used a fair amount in the Warhammer 40k gaming community, and I'm getting really sick of hearing it.
It's a term which is intended to describe a certain model or configuaration or tactic that unbalances the game and make it extremely difficult or impossible to beat. Warhammer 40,000 is a game that's constantly being tweaked and updated and balance issues are always being ironed out. The timeline for that to happen, however, is very slow. Often an imbalance can literally take years to address in the form of an errata or Chapter Approved update or what-have-you. Unlike a video game, where a downloaded patch can change game weight to be more balanced, Warhammer 40,000 has to be refined through very slow processes.
This means that there are going to be times when certain elements of the game can be manipulated in such a way as to gain an unfair advantage over an opponent. it's considered gentlemanly and good etiquette to avoid exploiting loopholes in order to unbalance the battle. Unfortunately, this is a soft science; there are no hard-and-fast rules for what makes something "cheesy". There are no "lines" that can be crossed or "standards" that can be transgressed. For instance, a player might decide to take three Wraithlords in a 1000 point game. God knows that in 1000 points it's nearly impossible to adequately knock off three Wraithlords in six turns, but it's still legal to field them because they fill the three heavy support slots and cost-wise you can still afford your HQ and two Troops. Yet, other players wouldn't necessarily be worried to see three Wraithlords on the table. For instance, a Ravenwing force playing Recon against three Wraithlords probably don't even have to worry about killing more than one - if that; their speed and numbers can easily win the game for them through points acquired in objectives. Therefore, is it okay to field those three Wraithlords? No matter how often a certain player would like to think that their own standards are self-evident and natural law, there really is no way someone can know for sure if they're crossing a line or not.
For my own purposes, I think of it in terms of hot and cold; if I feel myself getting a little warm, I turn down the heat. I can't say exactly what temperature that's always going to happen at, but when it starts occurring to me that I might be a little bit hot I assume it's time to pull back a bit on the thermostat. "Cheese" is the same to me; when I start asking myself "is this cheesy?" then it's time to consider trimming back a little. For instance, I won't take more than one Star Cannon for every 400 points. Some players think that's still too many, and others can't see why you'd have to limit them at all. In the end, however, it's about my contribution to a game that's fun to play for both people (handicapping myself is no better for the game than going cheese). When I start to fill up on Star Cannons, I feel like I'm overpowering my enemy in a way fromn which he or she can't recover, and so that arbitrary limit is one I use. I know that when I stick to it, I never have that "getting too warm" feeling.
Generally people don't use cheese in their armies and strategies all that often. I think of it in the same way I think about extraterrestrial life; I'm sure it's out there, but we don't see it nearly as often as everyone says we do. My perception is that the accusation of cheese outstrips its actual occurrance by a factor of a hundred to one.
I think about an example that came up recently. I sometimes field three War Walkers, each with two Bright Lances. At first glance, this looks formidable; they can bust a Predator or Land Raider a couple times over in one turn. There's no arguing that they clean up armored vehicles like few other things can, and I get accused of fielding cheese when they hit the table. I've had a finger or two pointed at my War Walkers and heard the name of a certain dairy product.
That usually gets a big, healthy "Go Fuck Yourself" in response.
A War Walker is armor 10 all around. Unlike a Vyper (which is also armor 10), it can take no upgrades like holo-field or spirit stones. They do have the same force field that Wave Serpents use (which reduces all weapons greater than strength 8 to strength 8). That's not exactly a coup considering that a Lascannon reduced to strength 8 would still have to roll a one on the damage roll to escape harm. Why use a Lascannon, though? A squad of 10 bolters seems to be all you'd need, likely hitting 6 times, and likely damaging the armor with at least one of those hits. And can those War Walkers get out of the way before they're shot? Heck no. They move 6" a turn (even a Rhino can move 12") and because they're vehicles they can be targeted past any infantry that might block their way. Due to the very nature of what they do, however, War Walkers must come out into the open... so without indirect fire and the ability to stick-and-move, those models are eggshells on legs. All for the cheap price of 300 points for a squad of three. Fact is... I rarely take them becausem, despite their terrifying ability to fire on the enemy, I just find them to be too weak and easily killed, thus handing a bucket of victory points over to my opponent.
My point isn't that War Walkers are or are not viable. I only want to show that cheese is in the eye of the beholder. The bias of the opponent who can only see what he has to lose by what pops onto the table is going to flinch and call "cheese" when people often forget to take points cost into account. Sure, a Scorpion Mark II tank can put D3 shots of Str9, AP1 (Blast) onto the table per turn, but the freaking thing costs 650 points. In most games that's at least a third of the army. Again, using the War Walker example, I love the power of what some models/units have to offer, but the points cost is just way too high. If, however, the points are low and the power/resillience is high, that can become problematic. This is one reason why Wraithlords can be sometimes employed in questionable, possibly-cheesy ways.
Ok, this whole ramble is going on a little longer than it needs to, but my point is this: I don't like being called cheesy. It doesn't happen often, but when it does it gets my anger up. For every "cheesy" model I put on the table, I pay through the nose. In my 1000 point tournament list I had only four models to deploy. They were resilient, yes... they were fast, yes... they carried great weapons, yes... and that's why I could only manage to get four of them. Meanwhile I'm looking at the enemy's Devastator Squads, or units of Necron Destroyers, or big, fat Death Squad (or whatever they call them in Blood Angel language), or the carpet of Imperial Guard covering the table. Lascannons and missile launchers and plasma guns all over the place. Four vehicles are not hard to crack under those circumstances, and every time one went down I'd lose as much as 220 points and a ~150 point squad inside would either suffer casualties or remain pinned.
Nobody calls you cheesy when they crack open all your vehicles and pin the passengers. They only call you cheesy when they don't realize they can deep strike behind and pop the vehicles in the butt (armor 10, you know), or if they forget to shoot the vehicle that got stunned last turn (so you can get that penetrating hit instead of just the glance) or they fail to take any fast units of their own (Land Speeders with meltaguns are the bane of my army's existence), or... or... or...
Anyhow. I'm sure I was going somewhere with this. Maybe I'll finish the thought another time. Off to play...