It also depends. If it's a good fight, let it go, at least until the friendly loses the advantage. If the friendly with the advantage couldn't hit the broad side of a barn and is clearly gonna blow it against a superior adversary (=if you see the icon "Dinger" above his plane), might as well dive in and save his sorry butt.
As for diving in to help countrymen, sure it's important. But you need to be able to distinguish between heroism and suicide. It isn't historically accurate to lose repeatedly entire squadrons of fighters because they all opt to save their buddy who went scraping the mud.
I remember one of the Brand W BoB scenarios, where I screwed up in a 109, got greedy and turned -- once -- with a hurricane. Soon there are .303s flying all over the place -- I'm in a cloud of enemies. I look up and see -ik- and buile circling 5000 feet above, like cruel gods, and I know that *I* screwed the pooch and there's nothing they can do. So I dive to the deck, and head, smoking, for the coast; fortunately, nor were the RAF pilots so suicidal as to follow me down.
Yes, it's imperative to help your buddies. But most warriors would rather be alive rather than make their bid to receive the CMH .
Here's a follow up question:
A high enemy engages you in 1 v 1, pings you, without damage, then flies off to harass a fellow countryman Co-E. Do you:
A. Forget about the insult and let them duke it out.
B. Go over and try to distract the enemy into trying to engage you again, to set up the drag.
C. Wait till the enemy blows enough E to get below you, then avenge the injury to your pride.
D. Wait until the enemy tries to dive away or even ditch, the friendly leaves (or sets up a BnZ pass), then go for the easy and merciless kill.
I think I've done about all of them at one time or another, often to the great irritation of my friendlies. I'm just wondering how many of you out there get sufficiently ticked to hunt down and kill those who mess up your paint job.