Would be nice to get some genuine input on the responsiblities of the Trailing AR. The mechanics are fairly simple, but what are the real responsibilities?
Primarily watch behind the referees back. Generally speaking don't watch play. The referee and lead AR have that. Keep an eye on everything and everyone behind the referee that they can't see.
Wait patiently until the ball comes back to your half? Nah, there's a few things you can watch for. Basically just an extra set of eyes at that point. Also, if you're on the teams' side of the field, it puts you in a good spot to try to calm down some angry coaches, if needed, sort of as a fourth official would do (assuming there is none).
Be sure to always stay with the last line of defence and don't get caught watching play too much. An assessor will pound you for not doing that. Watch everything going in back-play, and make sure the benches are in order if you happen to have that responsibility.