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

[Nagot Gick Fel]

In MP I usually buy 5 to avoid enemy scouts claiming my provinces unopposed, it costs only 15 gold and is worth the expense. I buy 10 where I want to deter enemy infiltrations. Sometimes up to 20 for nations that have good militia, like Jotunheim, in inner provinces I want to protect and where I can't recruit local troops (because of low resources). And only 1 for Ashen Empire and Soul Gate, so there's always a leader to lead the dominion-summoned troops.