The guest who is told to make themselves at home still has to discover which rules are unspoken.

Being told to make yourself at home is a genuine offer wrapped around an impossible instruction. Every household runs on rules nobody wrote down, about which chair, which cupboard, which hours are quiet, how loudly you may open the fridge. The guest has to detect all of it by trial, and the cost of a wrong guess is a small correction that makes everyone slightly uncomfortable. The warmth is real, and so is the guesswork.

When you are hosting, replace the phrase with two or three specifics: help yourself to anything in that cupboard, we get up late, the shower runs cold first. When you are the guest, asking directly is far cheaper than guessing wrong. Specific permission is what the general phrase was trying to give.