New to Panzer Campaigns, have many questions... Let's start with HQ's

[Mr Grumpy]

If broken and possibly isolated, would they offer any benefit or advantage to their subordinates?  Or would an HQ in such a situation be completely useless to it's subordinates as if it were completely eliminated?

In practice the end result seems to be that keeping an enemy HQ alive in those conditions is preferable to destroying it. A gamey move maybe, but the idea is to prevent the deployment of a replacement HQ.

Perhaps this is a little gamey, but everyone seems to have a different view on what "gamey" is anyway. 

I would only say that if the HQ sits in a stack with the last units from is formation you might as well destroy it and bag the points as it will never reappear.