Preformatted payload can be a big win for page speed, especially if your payload cannot vary based on request headers, or has only a few variants.
A special case of preformatted response used to be baked into microsoft IIS. If you connected to an address that could only redirect to another address, IIS wouldn't even wait for the request, it would just send the 302 response and hang up. This, it turns out, was not really compatible with Mozilla at the time, and may have violated some RFCs, but I kind of liked it as a hack.