[thejeff]

I'll position my forts based on chokepoints, resources, etc, but the reason I build them is mages. More forts -> more mages -> more research/more battle mages -> more effective battle magic/summons.

More national troops are good as well. More accurately, being able to recruit national troops close to the front line is good.

Protecting labs/temples so you can research/summon etc without worrying about raiders.

No real problem with setting forts one province apart. Just don't try to recruit from that province. Just don't put a fort next to your capital if you're relying on resource heavy capital only troops.

All that said, against the AI, I usually only get one or 2 forts built before I start taking them from the AI as fast as I need them. Can't think of any reason to demolish them, except to keep them out of enemy hands.