The transitional wardrobe solves the specific problem of a fixed-date seasonal swap: the three weeks either side of it, when mornings and afternoons need different clothes.
A minimum transitional set: one mid-weight layer, one light coat, one pair of closed shoes, and one pair of trousers that works in both directions.
Keeping these out through the changeover — rather than boxing them with the rest of the season — is what makes seasonal rotation practical rather than an annoyance.