I scaled down to a ~550 sq ft unit a couple of years ago, but had an interesting realization a few months after moving in that the walk-through closet that leads to my bathroom (maybe 175 sq feet together) could theoretically work as its own micro-apartment. I closed the door, and started mentally fitting a bed, mini-fridge, microwave and hot plate, and desk into the space. It all fit, give or take a half a foot here or there, and assuming a bit of custom storage.

Admittedly, though, I must have limits for small living spaces. My favorite part of this exercise was opening the door back out into the rest of the apartment, upon which my studio suddenly felt palatial.