If your nsec ever gets compromised, whoever has your nsec can access all of your DMs. One of the reasons I like Keychat is that it uses the signal protocol which provides forward secrecy and it’s super easy to spin up a new ID to chat with someone. You can initiate a conversation via normal Nostr DMs if you normally use a client like Damus, Primal, or Amethyst and then easily move the conversation to Keychat using a separate identity.