Circulation
The floor space used purely for moving through a home — corridors, passages, the swing of a door, the gap you walk between furniture. Necessary in moderation, but the first place wasted space hides in a compact plan.
The first thing to question
A long internal corridor in a small flat can eat 8–10% of carpet area while serving no other function. Subtracting or absorbing it is often the single biggest space gain available.