1. Lairing makes a huge difference. Everything seems significantly less buggy this way, and there's a lot less lag when the player loads the site.
2. All creatures will start gathering at meeting hall zones one by one (This also counts structures designated as meeting halls. It won't remember their owners, though).
3. Dwarves and other sentients will only be scattered into places they can path to from the above-ground map edge (same with subterraneans and the underground map edge. If this includes massive open caverns, or, say, a ridiculously deep curious underground structure, then practically the whole fortress will end up down there. Recall that NPCs cannot path through water or open spaces, but adventurers can
4. Fortunately, you can keep dwarves and siegers out of undesirable regions simply by walling them off, building structures in their way, channeling out pits or pools of water and retracting any bridges over them, using floodgates, raised bridges, or even forbidden doors. However, you have to make sure that dwarves can reach the meeting hall from the edge of the map, otherwise they'll just appear outside and be stuck there. Unfortunately, this means locking dwarves/monsters in rooms or isolating the fortress and its inhabitants from the outside world will not work. You can still fill them with monsters from the deep though.
There could still be problems if the adventurer decides to take a nap after opening the way.
5. Dwarves in active soldier mode at the time of retirement will stay that way, and thus behave like soldiers. Incidentally, they will also be easier to recruit as a result.
6. Dwarves will automatically be given weapons befitting of their profession. Peasants will be given knives and soldiers will be given weapons and ammo.
7. Many of the undead in the circus tent get scattered into hell, and the HFS beneath get pushed all the way to the bottom, regardless of whether or not you can get into the place. Meaning nobody pops out when you grab the sword
I suppose you could get around this by finding the tent via embark, embarking
near but not on top of it, and opening a path to it through the caves.
Demon infested fortresses are more fun, anyway.