well your bare legs are on the jeans… and i’m sure your underwear smell enough to pass by touch….
it depends on how much stain is on the outside… a lot of people almost never wash their jeans.
there’s also any printing, and and kind of wear would be better on the inside… like fuzziness or messing up stitches…. it basically keeps it looking newer.
i’m too lazy for all of that but i do always zip up any zippers so they don’t distort from each other when hot, or snag anything else.