note: lobpot thoughts ahead
kind of necro sorry. Another situation in which things get complicated is where you've just captured a reclaim field but your forces are wounded. I think that repairing your units will mean they can hold that position longer and allow for more reclaiming. Your enemy may have even fallen back to repair so it can wipe your force out. If you're caught up in a battle to secure a reclaim field and you keep losing units, then you're making that reclaim field continue to exist and if you lose that fight, then you lose the field. Usually a reclaim field (between two armies) is not worth an entire army or even a good part of it, especially losing that army + the enemy getting to reclaim it. Also I think generally you want to reclaim wrecks further away from your lines (that you can access without getting blasted), since those are the ones you are most likely to lose access to in the near future, and you can deny the enemy access to that metal.
I think throwing down caretakers really quickly might be a play (with terraform in front of it to block shots, ideally no tremor) so that your cons don't have to get too close and you get a ton of extra BP really quick so that your cons can focus on repair, or even setting up defenses with the huge metal flow you get from caretakers. If the enemy is applying too much pressure, quickly reclaim the caretakers before you lose them (10% loss of metal vs. 140% if the enemy takes the territory and reclaims the wrecks). You could even have the caretakers reclaim themselves. Caretakers are cheaper BP anyway so losing them isn't really a big deal compared to losing an army of mobile constructors, which has much more value. They make cost in metal every 18 seconds!
Steel_Blue, I feel like that situation only comes up earlygame, in which case you should probably be focused on expansion like you said since a damaged raider can still retreat micro and occupy territory, and getting the con to repair the raider is a time-consuming task. If you can quicky repair something on the front (cons are nearby) though, you actually spend less energy per the metal you saved by repairing than if you lost the unit but reclaimed the same amount to build a new unit - assuming you can reclaim still, since that unit's death could mean your loss of the field, the con reclaiming, etc, and the replacement will take some time to arrive.
