I've been thinking a bit recently about casualty removal, and how to place your models to greatest effect at what time within a game, which resulted in me having a thought i initially discarded as being daft, but which kept niggling at me as being worthy of consideration.
The basic principle behind my thinking is this: 'Does my heavy weapon specialist ever become a disposable asset?'
'Of course not' I said to myself, 'I've paid good points to get that multi melta/lascannon/dark lance etc, he's going to be the last model to die!'
But then i thought again, if I've got a lascannon in a tactical squad, it's there for one purpose - killing tanks/walkers and other generic model types with armour values. Well, what happens if I have a really good first couple of turns shooting and get rid of all my opponent's models with armour values? I'm now stuck with a heavy weapon that limits my squad's mobility, and is optimised for shooting at targets that no longer exist. Sure, a lascannon will make a big hole in an infantry model, but is shooting it stopping your tactical squad from moving to claim an objective, or getting into rapid fire range to mess up that cultist unit sitting on an objective. Does that one shot prevent the rest of the unit from making a difference in the game?
I guess experienced gamers will already have guessed the point I'm making, which is not that the points for such a weapon are wasted (in fact, if you check out my 'Dangers of becoming a specialist' article, a marine tactical squad can actually become a specialist unit without too much effort, making that heavy weapon far more useful). It's recognising that point in the game where the heavy weapon ceases to become an asset and becomes a hindrance to winning. When you recognise that point, stop the unit standing still, put the heavy weapon bearer at the front and don't stop to pick his gun up if he's shot down.
In an effort to provide a bit of balance to that idea, I'd like to share with you an event from a league game of mine recently at my local club. My Dark Eldar were getting very outgunned by an Imperial Guard detachment, and a full squad of warriors were stranded in their raider transport in the open with little else to distract the enemy. Sure enough, the raider got wrecked and the explosion and subsequent fire whittled their numbers down to three, who'd had to hit the dirt to stay alive. Two of those still alive were carrying darklight weapons. In my following turn, the dark lance bearer (who'd gone to ground and was therefore limited to snap shots only) took aim, hit the Leman Russ Demolisher in the front armour, penetrated and blew up the offending tank. Of course I still lost the game, but that one shot reminded me why it's sometimes best to arrange your models to protect the heavy weapon bearers.
So of course once I'd thought of that, I started thinking a bit more about the idea of expendability. It's probably more appropriate to the idea of tactics more so than expendability, but what do you use transports for? 6th edition seems to have generally resulted in the accumulated wisdom of the internet suggesting that transports aren't so great anymore. I've got 4 razorbacks sitting in one of my marine collections though and I'm sure as hell not going to stop taking them yet. I'm struggling to think of a better way of getting my tactical squads across the table that quick, particularly when it can then anchor down and become a line of sight blocking pill box once it gets where it's going. And that's my point, once i've disembarked my unit from the razorback, does it become expendable? Well I'm certain I'd rather my opponent was shooting their plasma guns at that than the objective-grabbing unit behind it, regardless of how much I've paid for a turret weapon!
In conclusion then, i would say that most units are expendable in the right circumstances, even terminators, but the crucial part is knowing when they become expendable, and being sure that they're not going to become invaluable again later.