ADDENDUM:
Starfleet command is NOT Brazil, Oceania or straight out of a Paranoia role-playing game. In contrast the Star Trek universe emphasize humanity and rational decision, so I do not accept counterarguments that somehow vital components are bizarrely twisted or ignored.
Answer 1) What does it mean to have "command" or being a starfleet officer? It means that you as commander must(!) decide what course of action is appropiate for a situation and (s)he has the responsibility not only for the own person, but for the crew and even for the starfleet! It is the very definition of "command". If you are unable to decide, the ship has the same state as being non-existent. Such a situation is even worse than being dead as commander because in that case you could have been replaced immediately. This is also a prerequisite as starfleet officer because at any time your superiors can die or stop being approachable/reasonable you must replace them. This is not only true for starfleet, but for any organization. If there is a chain of command, the ability to decide (even if it is wrong) is absolutely vital and not replaceable by any means.
There are several key components which makes this vital. If a conflict is possible (this does not only apply to military but also to all branches where you come in contact with possibly hostile counterpart) and there are no rules at all, you cannot communicate your intent. The enemy surrenders? Could be a ruse. The enemy retreats? Could be a trap. But it also applies to the own position. You really want to give up, but you faked surrender before? Good luck to convince the opponent. This is the important idea of the red phone. During the Cold War the USA had always bombers with nuclear bombs moving around the Soviet border to guarantee second-strike capability. The interesting part is now that those bombers without any treaty deliberately moved in a predictable path so that the Soviets were able to track them. The idea is that, yes, you have a threat in the air, but you give your opponent the chance to react if something unusual happens (Hey, your bomber is moving toward us! What? We call him back. It still moves toward us! We lost contact, repeat, we lost contact. Shoot him down, here is all available information about his targets and path!).
Another key component is that you as organization have acquired a long experience what strategies and tactics work or don't work (Those can being different depending on what organization you have. Even with the very same goals and organization structure, but different people the strategy can be different!). Those are also coded e.g. in the rules of engagement for Starfleet. A commander who ignores them in a simulation(!) cannot be trusted to follow them in reality which will bring other ships and starfleet into trouble. In fact, in one episode of Starfleet Benjamin Maxwell of the Phoenix despite being a brilliant captain was court-martialed for unauthorized strikes while it was later revealed that he was completely right that the Cardassians were violating the treaty.
This does not mean that rules of engagement are followed. If a party has an overwhelming power, it could decide to ignore them because there is nobody who can challenge them. Also if a party is on the losing side, it is tempting to throw any rules overboard to get one attempt to a decisive advantage.Any fighting member of a military organization (yes, starfleet ships have phasers and photon torpedoes and those are weapons) must face the consequence that death is not only possible, but often very likely. While recruiters may have "forgotten" this fact in their presentation of free extras and being a tough guy, it is uncomfortably valid. Now the standards vary from organization and task (scout? stormtrooper?), but if you don't accept a reasonable risk to defeat the contrahent when it is not only possible but very likely in a military organization, you fail.