I'm not sure what the correct terms are, so I'll refer to in-app/in-client notifications as internal notifications and mobile-style out-of-app notifications as external notifications.

Based on what people usually refer to with the word "notification" in the context of social applications and messaging services, and your comment, I'm assuming you're talking about external notifications. If you mean all notifications in general, I've misunderstood your point and can ignore the rest of this comment. I do think that internal notifications are useful.

I'm not saying that external notifications are useless, but rather that I don't feel that they're as important as you seem to make it out to be.

Also, even if your Lemmy client doesn't support external notifications, Lemmy supports RSS, which you can subscribe to with a different application.

It should probably facilitate discussions then

Discussions do not have to be between only two people, others can continue where someone else left off.

People often need to continue conversations to clarify information & elaborate…

This is true, but it doesn't require notifications outside of the client. For example, I noticed your reply as Lemmy's web UI showed that I had an unread message.

I don't mind continuing a discussion over multiple days, though I'm not sure if this applies to everyone.

Shades of Mastodon users justifying suicidal design choices that were later rolled back here.

Could you elaborate? I don't use Mastodon, as I don't see the value in "micro-blogging" and prefer to follow topics rather than people.

As for the rest of your comment, I too disagree with blocking VPNs & Tor to fix their CSAM problem, but I don't see how that is relevant to this discussion? Though I do not mind if you want to discuss that instead.