I am with 737 Jock on this... As a captain, I feel entitled to interfere not only when safety, but also when the efficiency of the operation is compromised. Sadly, I have found some F/O's seem to be annoyed, especially cadets, who tend to add a safety margin over a safety margin... and then another one "just in case", without really being able to explain why...
While I understand that someone with low experience tends to be cautious, I am surprised by attitude of some of those guys, who think they can do whatever they want "'coz it's their sector" and don't want to take any critique/advice etc...