Continued from here.
The final round of mead was poured out. Lord Gusorio was looking fairly tipsy, and his small audience were feeling the mead spinning in their heads as well. But when the baron launched into one more bit of advice rolled into a tale of his adventuring days, they came to attention and made sure to remember what he said. The stories he told could save their lives.
The baron said, "After we'd been scouting the fourth level for some time, we realized it would take too much effort to haul all of that treasure up to the surface, at least until we'd found the secret exit we'd heard rumor of. So we ended up clearing out a small section with only one entrance. Shalea magicked the door. We posted a few of our men-at-arms as additional guards. Then we had ourselves a nice little fall-back point on that level. We went back to town, gathered as many supplies as we could, and stocked it well.
"Whenever we found a bit of treasure on that level, or on the fifth as well--it took us some time to find that secret exit from the fourth--we would bring it to our strong point. Of course, having that strong point meant we needed to keep it supplied, and we had to pay quite a bit extra to all the men-at-arms who guarded it. But it saved us the trouble of having to lug all those coins all the way up every time we secured a treasure chest..."
Sometimes, you want to make the dungeon, or at least a small part of it, your own. In Gary Gygax's original Greyhawk campaign, several of the prominent characters cleared out and took over the 1st level of that dungeon. They stocked it with their followers, and then charged a tax on other adventurers venturing through.
Maybe you don't need to take over an entire level, but taking and holding territory within the dungeon can be beneficial. As Zanazaz pointed out in the comments to my original post in this series, a dungeon can make a great bolt hole for PCs who've gotten in trouble back in the hometown. It's hard enough to find men-at-arms willing to venture forth with a group of adventurers. The local law enforcement officials will have a hell of a time trying to get a posse of Normal Men to go track them down.
As I posted in my example, strong points within the dungeon, held by a combination of magic and steel, make for the ideal place for treasure to be stored, healing and spell rememorization to be done, and so on.
And sometimes you might just want to clear out a hazardous area of monsters, then seal it shut to keep them from coming back, and to keep anything new from moving in in the future. Most Megadungeons are so big that clearing them completely would be near impossible, but small sections can be managed in times of need.
Of course, the group venturing forth to conquer some part of the dungeon is going to need to be ready for quite a bit of combat to get rid of all the monsters in their chosen section. Spells that can bar access, like Wizard Lock or Wall of Stone are good choices, too. And a bunch of Elves, or a wand of secret door detection might also be a good idea. It won't do much good to secure all the obvious entrances to your new mini-lair only to have a secret passage you don't know about inside it.
Of course, making that lair behind an already known secret door is also a great idea. Especially if you can find an area with several small rooms behind it, and no other secret entrances, you'll have plenty of space for bunking down, storing gear and treasure, and setting up a small kitchen area. Watch out for ventilation problems, though, especially if you have one of those types of DMs who wants you to worry about that sort of thing...