It can be turned off. You get a pop-up as soon as you open the site.

I’m on the other side of this and I think this is a great social feature for websites.

One thing the web currently lacks is multiplayer mode, and this is one way of doing it.

It does make more sense to have something like this in sites where you can move things, and canvases, but I do think it would be nice to have this + a chatroom in websites. Some sort of “good old internet” feeling.