Here’s my two cents - I’ve been thinking on very similar lines to trihero’s initial post. It comes back to my main mantra of valuing units over territory (but you still need to hold & gain territory, don’t get me wrong - it’s just easier to do if you have more units :) )
These are my considerations:
1. Will leaving an Inf add pressure to the enemy’s resources? It may be a net loss but if it gives the Allies more to do with their limited resources, I’ve just made other battles harder for them because they have to commit some air power to this one. It must be remembered that as Germany you are not only trading with Russia, but also with the UK and possibly the US. So yes Russia only has two fighters, but the UK has fighters, a bomber and a battleship.
2. Can the allies shore-bombard the territory? If yes, leaving an Inf is not as useful as normal, since it has only a 1/3 chance of even getting to defend.
3. Can the allies tank-blitz the territory? If yes I may be more inclined to leave an Inf there, because otherwise they truly can get the territory absolutely for free. However alternate tank blitzing by each side may be better for me, if I am more in need of conserving units than the other side.
3a. Can the allies send tanks through that territory to attack something else that they couldn’t otherwise? Eg. Russia might have tanks in Karelia, and Inf in Caucasus - If belo is left empty, both forces can attack Ukraine.
4. Can I afford to trade units more than the other side? If my production is inferior, I need to save my units for big battles where I can effect a significant swing in total IPC unit value.
So, like others have said, it depends on the circumstances. I find myself leaving the Inf more often than not though.
Finally, I’ll just say that my favoured attack for trading territory is to match the number of Infantry, and add air power. So e.g. if a territory is defended with one Inf, I would attack with 1 Inf + 2 Ftrs, or maybe 1 Inf + 1 Bomber, or more air if I have it available. I will only send 2 Inf if the territory has tactical importance. If I am just trying to get the IPCs and kill the enemy unit (the unit being more valuable than the IPCs from the territory, as an active, front-line unit), I just match the infantry.
The reason is that I don’t want to get 2 Inf killed in order to kill 1 Inf - that’s bad.
Here’s how it works out:
Attack with 1 Inf 2 Ftrs v. 1 Inf:
- with total punch of 7, good chance of killing the enemy Inf - + 3 IPCs for me.
- 1/3 chance of losing my Inf - -1 IPC for me
- 2/3 chance of taking the territory - for a 3 IPC territory, that’s +2 IPCs for me, + a 1/3 chance of killing a counter-attacking Inf - another +1 IPC for me.
- I will lose the Inf to the counter-attack: -3 IPCs
Total net = +2 IPCs
If you attack with 2 Inf 1 Ftr:
- Less likely to end battle in one round. IF the enemy Inf lives another round, they get another 1/3 chance to kill an Inf. But this is a small difference, punch of 5 instead of 7.
- taking the territory is more certain, so I award the full +3 IPCs for trading a 3 IPC territory - +1 from my plan above.
- You have now got 2 Inf occupying the territory. These amount to two 1/3 chances to kill enemy Inf instead of two, so that’s another +1 IPC
- Both occupying Inf however will be lost to a counterattack: -3 IPCs compared to above
So for this attack the total net is +1 IPCs.
That one IPC difference may not seem like much, but if you trade three territories / turn like this for 10 turns, that’s 30 IPCs! Suddenly by round 11 it is as if you have had one extra free turn of producing Infantry!
However, the 2nd attack may be good if you are wanting to trade more units, which you want if your side has a unit lead on land. eg. suppose I have 80 units, and you have 60. If I can keep trading off evenly until I have 40 and you have 20, that’s good for me.
But generally I like to think that I will put my surviving units to better uses than my opponent will, so I try to keep my own units alive as a priority.