I like enough realism to allow for suspension of disbelief; eg most monsters need access to a water source & food. If I have Chokers & Darkmantles (especially) in a dungeon, and they weren't placed there by the BBEG, I'd like it to connect to the Underdark or otherwise be within a large cave environment - maybe a deep rift. Neither of those travel overland. Rats & dire rats can be almost anywhere though, and will cluster around inhabited areas to feed off the garbage of other creatures.