Technically a put or a patch is also idempotent. The benefits are idempotent and safe (and semantically appropriate). Post (generally) communicates something is changing whereas a query doesn't
PUT is idempotent, PATCH is not always. The semantics of a PATCH payload are up to the server and standards like JSON Patch (RFC 6902, https://datatracker.ietf.org/doc/html/rfc6902) allow non-idempotent operations like adding an item to a list.
