In case of plain HTTP over TCP, there is even a hint in the spec about why and how a server might want to avoid fully closing prematurely.
https://datatracker.ietf.org/doc/html/rfc9112#section-9.6 (this was already in https://datatracker.ietf.org/doc/html/rfc7230#section-6.6)
This is relevant if the client sends multiple requests but the server decides to close the connection after one of them. The server should discard the additional requests until the client signals no more requests are coming.