You often read that a "boring" feature of dungeon design is the empty room. They are considered by some a waste of space on dungeon keys and on dungeon maps. That's because folks don't understand the utility of the empty room.
Empty rooms do build tension, empty rooms expand the feeling of size, empty rooms build atmosphere, empty rooms provide a place to hide and empty rooms provide battlegrounds.
The utility of the empty room to build tension is obvious it's an easy cure for "a monster behind every corner syndrome". It breaks up the pattern of open door, kill everything inside and loot, breaking up patterns builds tension as it forces people to think about what to do next. Wandering monsters don't just roam corridors and tunnels they also wander into rooms, is it worth searching a seemingly "empty" room and risking begin stumbled upon mid search, or alerting an un-empty room next door?
The use of the empty room to describe space and build atmosphere is simple: this dungeon is so big nothing has claimed this space…yet, this dungeon is so ancient and abandoned no one else has stumbled upon this chamber in decades, the feud between the orcs and goblins has force them to abandon this are, etc…
The empty room fills things out and suggests reasons for why the room is "empty".
The empty room as place to hide is very important if playing a game where folks are paying attention to fatigue and encumbrance. If a party must rest they must have a place to rest. If there is too much too to haul out while romping about the dungeon exploring and tangling with threats it sure is useful to have a place to stash the loot others aren't' paying a lot of attention to so you can carry the load out later. The empty room is a place for the dungeoneers to claim as their own even if for a short while.
The empty room as battle-ground is useful as a place to draw fights from occupied areas. It's hard to ambush monsters in their own lair, it's not so hard to do it 200' feet away in a different area. If one has a dungeon with various competing factions and chatty negotiating players the empty room also play a good spot for settling duels and battles; few folk like hosting a battle in their living room but they can be talked into fighting in some other space.
The empty room is a feature of a large and dynamic dungeon that shouldn't be considered the product of over eager map drawing or lack of imagination as the empty room is a feature of much utility to a dungeon based game.