• Double stairways: every apartment must be connected to at least two sets of stairways, this rule comes from a time when fire prevention was lacking, but nowadays it only gets in the way of designing units with more rooms/windows because geometry.
• Maximum floor space: what it says on the tin. There is a maximum set of space each floor can use and this incentives making narrow hallways and make away with communal spaces in favor of packing as many small units as you can.
• Building setback: every building needs to be a set amount of space away from the sidewalk, which means a lot of space in every lot is wasted as it legally can't be used for anything. Without this rule you could design adjacent lots to share a big courtyard that can be used as a community space.

https://urbanarium.org/decoding-density