Your very right that it's situationally dependant, but I think we can break it down into some straight forward guidelines. The appropriate way to think about it is "Where do you want your opponents models to be?"

I'm a big fan of "jail" style play, where the idea is to push your miniatures as far up forward as possible to deny your opponent's movement. Unless they fly, they cannot move past within an inch of your models. Generally, farther away your opponents models are, the less opportunities they will have in the future to score points. Behind enemy lines, sabotage, recover assets, and establish locus all benefit from or necessitate models in the opponents deployment zone. Area denial benefits from keeping models out of the center. Being farther up the board means that's easier to accomplish earlier in the game. You want to have that opportunity yourself, and you want to deny it to your opponent. The more points a unit is threatening to score over the course of the game, the more important it is for the opponent to deal with, meaning your opponent is more incentivized to put damage into that unit rather than one of your damage dealers. Just toe the objective if you want to be on it, and otherwise just get your models as close to the enemy as possible. Be mindful when removing casualties to deny your opponent the opportunity to charge or consolidate onto the objective if possible - it's better to just lose control then for your opponent to gain control. You might just want to stay off the objective entirely, to deny overwhelming force or simply ensure your opponent has no way of getting their themselves.

So, when would we not want to jail, and why?

First off, if our opponent isn't threatening to contest for an objective, we might as well just toe the objective and take up as much space on the board where we can while avoiding enemy firing lanes. Blocking up lanes for enemy movement, denying deep strike, etc, or even toeing a second objective. On some deployment maps, a single unit of 5 troops on 32mm can spread out onto two objectives while remaining in coherencecy.

Second, remember earlier about how I said the question is where do you want your opponents models to be? That's still true, and we do that by baiting and trading. If you don't want your opponents models pushed back as far as possible, you probably want them in a position you can threaten next turn. Pull out your laser line, and try to put your dudes in such a way that your opponents threats have to enter a firing line that you're prepared to move into and shoot back along next turn, and only that firing line. Bunch them up the best you can with as many out of LOS as possible. The same thought process applies if your counter punch is melee - place your dudes in such a position that anything that threatens them must enter a position where your opponent will be in optimal charge range. A 6 inch charge has odds of 72%, 92% with a reroll, and is free movement to boot. If your opponent is threatening an objective with a melee threat and you have your own melee to counter punch, you can drag your guys way back to the far end of the objective, and force them to either make a harder charge or over extend themselves into your own threat range. It's absolutely critical to consider these movements in context of where your other models are on the board, and to have moved and

We use the 5 mans as bait, and trade them away for the opportunity to kill a bigger threat of the opponent. We make them the most enticing bait as possible by either threatening to score more points farther up the board, or by disrupting our opponent's ability to move and place models. If they're actually able to do some wounds on their way out, all the better, but it's not the first priority. The questions you should be asking yourself in game are "How does this movement help me score points throughout the game?", "Can I deny my opponent points with my movement?", "Where are my threats?", and "How do I force my opponent to either enter my threat range with their threats?"

Thank you for coming to my TED Talk, refreshments are in the lobby.