The websocket implementation was streaming federated data to the UI in real-time, and was responsible for a bunch of bugs/UX issues that wouldn't have been evident when there were less people on Lemmy (such as scrolling down New posts on the homepage and seeing them zoom off the screen and back a bunch of pages as new federated posts from busy instances rolled in)

Some instances were also hitting the open socket limit of their reverse proxies IIRC, which was causing some users to get stuck on a spinning loader indefinitely.

I personally used an app instead because of the bugs/ UX issues caused by the websocket implementation, but since the 0.18 update on my instance the site is so much nicer to use.

Edit:

Websockets largely have a lower compute cost per request, HTTP requests are slow and expensive vs just firing off data in an already established TCP connection, so this isn’t tracking for me?

Most browsers send keep-alive headers to request that the webserver keeps the TCP connection open - I believe for HTTP/2 and HTTP/3 the connection is automatically held open regardless. It doesn't address the overhead caused by resending headers etc, but it's faster than establishing a new connection each time, and 'manages itself' by closing the socket automatically after a period of inactivity.

Websockets are still undisputably faster though, but I think it all comes down to implementation