Indeed, especially with websockets. It usually adds some latency based on the poll frequency, or just a bunch of repeat requests.

I've read in some NWC code, I believe, some form of notifications on the subscription to the relay, but haven't read more into it yet. It may have been in the nostr:npub1getal6ykt05fsz5nqu4uld09nfj3y3qxmv8crys4aeut53unfvlqr80nfm implementation or a fork of satdress. NIP-47 doesn't mention anything atleast.