As others have already said: Yes, it is useless in terms of cache. Besides it being useless in terms of cache, it also incurs other overhead. Another DNS reque

As others have already said: Yes, it is useless in terms of cache. Besides it being useless in terms of cache, it also incurs other overhead. Another DNS request, another TCP handshake, another TLS connection. With HTTP 1.1, this might still make sense because you don't get resource pipelining, but with HTTPv2, the extra overhead is simply extra overhead. With HTTPv3, it becomes even less useful to have the domains sharded. Generally speaking, the best use of resource usage with the modern web is to serve everything from the same domain.