My office is approximately fifteen feet by twelve feet in size. That is does not produce an even number of five foot squares. The most common interior door width is thirty inches, not five feet. This causes problems with a gaming system that uses five-foot grids.
I started playing Dungeons and Dragons years ago when stationed in Europe. I used millimeter graph paper instead of the five-squares to the inch most gamers in the United States used. I picked up a 0.3 mm mechanical pencil. They are not as common as the 0.5 and 0.7 mm pencils you find today. I used 1 mm equaled 1 foot. All my walls were one foot thick, similar to the thickness of the walls found in old buildings in Europe.
This allowed creating dungeons that are difficult to map on standard five-squares to the inch graph paper. For example, just make a series of square rooms that are twelve feet wide with one-foot thick walls. If you use a little variety, some rooms are twelve feet wide; some are fourteen feet wide, and so on. Players trying to map the dungeon have a difficult time getting the scale correct. This allows hiding a small treasure room in-plain sight. Slipping a two-foot deep treasure room between rooms is easy. I know how much junk I can cram into a two-foot deep closet. Picture Fibber McGee's infamous hall closet.
Departing from standard five-foot squares causes havoc with games like Dungeons and Dragons Fourth Edition (4E). I tend to be a devious dungeon master. I enjoy running a game where the party kills themselves. I was running a campaign where one of the player characters loved to use a fireball as his first defense. If anything happened, you could bet the wizard would cast a fireball. I created a dungeon specifically for that character.
Instead of your standard five-foot wide hallways with eight-foot ceilings I created a dungeon where the main hallways were only thirty inches wide (2'6"). The ceiling was only sixty-six inches high (5'6"). This allowed most characters to slide into the dungeon. A small band of creatures about ten inches tall, looking like Barbie dolls attacked the party. The creatures then retreated into their lair. The party took the bait and followed. I worked out the entire volume of the dungeon beforehand. A fireball from the wizard filled a larger volume than the entire dungeon. The main corridor lead to a small circular room about four-foot in diameter. Around the main chamber had three tiers, each about eighteen inches high. This allowed a large number of the Barbie dolls to attack using small little bows.
The logical solution was to retreat. Instead, the wizard cast his fireball. The dungeon exploded. I believe only the fighter survived the blast and the damage from the collapsing dungeon. He received a lot of experience for the death of hundreds of Barbie dolls.
The point is there is no way to play that adventure using five-foot grids.