border management and defenses - do you use them? up to what value?

[Ygramul]

How do you manage your borders while you go fight a war in another corner of the map?

I also bring up the defense of the newly conquered provinces to 10. I find that with a decent income bordering provinces can be raised 20 or 30
(sometimes 40 : 30 -> 40 costs ~$350 ). These can hold of moderate armies by themselves while I fight a war on another front. It sucks of course if you loose the war with a 40 defense province as this means loosing $820 worth of investment.

Do you folks instead use local garrisons? Does all this change greatly in the late game? (where I have never been yet)

Yg.