True that. The most awkwardly obvious one for me is probably this guy in
The Enterprise Incident. A full commander who outranks everyone on the ship except Spock and the captain -- yet he just stands there without any lines or reactions during a tense crisis in the briefing room.
Production-wise, it was probably a costuming oversight, or maybe just the consequence of being the only uniform that day in the needed size and color that wasn't in the laundry or something.
In my headcanon, he's not a member of this crew. If he were, then based on rank he should be chief engineer or chief of security, and should have been called on during the briefing. Or at the least, if they didn't want to pay the extra for speaking, Kirk could've said something like "Commander Smith, have your security teams ready for boarding if necessary" and the guy could've acknowledged the order with a determined, confident head nod.
Anyway, instead of all that I assume he's a dude from some other starship who's being ferried someplace by the
Enterprise. A crisis meeting is called and he naturally attends to see if he can help. However, unlike all the visiting bureaucrats who always want to tell Kirk how to run his own ship, this guy is a seasoned Starfleet commander who will jump in to help in an instant, but respects the chain of command and has the experience to listen, think, and wait until he's called into action or has something to contribute that nobody has pointed out yet.
It's a shame, though... a non-white actor in a high-ranking position could've been more than just a background prop, using as little as a single line of dialog.
EDIT TO ADD:
Ha! I just went to watch this scene again and realized I'd always been so focused on the Commander that I never noticed there was also a Lt. Commander extra. That makes me wonder if this was actually intentional, like maybe the script directions were something like "this is a big deal; put some important-looking extras in the room"?
Now that I think about it a little more, given the gravity and secrecy of Kirk's mission to steal the cloak, maybe these guys are actually Starfleet brass, or Section 31 strategists, or emergency spin doctors or something that are just
disguised as officers from some other ship catching a ride on the
Enterprise. (Recall that in this scene, the crew is not privy to Kirk's mission yet.) The high ranks are there to ensure that if they need to step in and do something, the rest of the crew will have to comply since Agent Red will outrank everyone else while Kirk and Spock are away on the Romulan ship.
Heck, in the case where Kirk and Spock fail, maybe these guys have orders to destroy the
Enterprise rather than let it be captured, should Second Officer Scott (see what I did there?) fail to follow Kirk's orders to that effect.