Unfortunately, this is not always the case. A couple years ago, I tried to check in with the CA while jump seating on a Delta flight. The MX guy was standing in the cockpit door way talking to the pilots, so I couldn't get past him, the gate agent and FA is rushing me telling me to take my seat (since I was the last one). I waited until I was the last one off the flight, and told the CA on my way out, I tried to check in, but he was busy with the MX guy and the agent and FA was rushing me to take my seat. I said Thank You and walked off. The CA followed me down the escalator and gave me an ear full about always having to check in even if i got a seat.