I think signing in with a node is essentially different from communicating via a randomly generated one-time-use nostr key By signing in with a node, you can send notifications to my account with confidence that I will see them the next time I log in, and you can log my sessions With a one-time-use nostr key, if you try to message me, I won't see the messages because I never sign in with that key again, and if you try to log my sessions, you'll only see one session