The other reason: you have an open TCP socket that you're actively using. Unless you finish with that connection or it breaks, why would you re-resolve it when you're not running connect() a second time? The failure mode we noticed most when looking into why clients weren't following DNS changes isn't that they were long lived connections, like a server copying a large file or streaming logs. Which isn't unusual if you think about it, just not a short lived web browser or curl-esque connection.
