Importantly IMO is the extra phishing protection that the UX is really nice if and only if the url matches what's expected. If you end up on a fake url somehow, it's a nice speed bump that it doesn't let you auto-fill to make you think, hold on, something is wrong here.

If you're used to the clunkier workflow of copy-pasting from a separate app, then it's much easier to absent-mindedly repeat it for a not-quite-right url.