As the title says - if you try to, or do, implement "one in, one out" rule when editing your wardrobe, how do you decide what goes out?

One obvious thing would be replacing worn out items or replacing items of lower quality by the more quality/luxury/versatile ones of the same kind (e.g. my H&M button down would go out if I'd find BB like the one Angie wears), but I'm thinking more about wardrobe additions of other kind.

E.g. you find nice new dress, but don't have other dresses to take out in order to make room for the new one, what goes?

Does removing "one" pair of shoes to make room for "one" new dress/skirt count?

To cut the long story short, what does "one in, one out" look like in your case?