What do you think about them actually LIVING? Sleeping during the night, eating in groups, drinking, playing games, doing some sort of work (such as having a group sorting loot), having meetings to discuss their dastardly deeds,etc.
Basically this would, depending on dungeon design and loot placement, potentially make dungeons harder. Instead of intermittently encountering single bandits, you would sporadically encounter groups of at least 3.
Also, I hate to say it, but it would also add a "sense of realism/believability/immersion."
Thoughts?