The mission briefing scene exists for one reason (with a corollary); it is to let the audience in on the plan, so they won't be confused by what people are doing during the mission.
The corollary is that the audience knows when the mission has gone sideways, when some traitor is doing what they should not be doing, when there is a surprise development (something unexpected happens) or something they expected to happen doesn't happen, and the team has to improvise.
The mission briefing sets up these tensions. It can be skipped altogether if the mission is straightforward. Famously, the Knight John Marshall (1140's true badass) was asked by a comrade what his plan of attack was to take down a troop of men. Marshall answered, "I plan to hit them with my sword."
Okay, mission briefing accomplished!
Mission briefings technically exist to ensure everybody knows their roles and what to expect, and what the backup plans are, including retreat. That stuff is boring when you can just show the action.
In fiction, mission briefings exist so the audience will not be confused and bored as you cut to various things going on. For example, the true mission is to hack a satellite, the distraction is a frontal assault they cannot win. You don't want the audience confused about what the heck is going on as you flash cut between the frontal assault and your hacker struggling to break the encryption, or she is surprised it isn't (as the briefing assured her it was) an XYZ encryption, but a triple X* encryption! She informs the assault crew they need to buy her 15 more minutes! Then 5 more minutes! Okay, they're getting killed out there and have to think on their feet.
In fiction the briefing sets up expectations for the audience, so your scenes and surprises make sense.
But, this doesn't always have to make sense right at the briefing. In Ocean's Eleven, for example, most of the movie shows people making the plans, but the audience is not clued in to the full and final plan until the actual heist takes place.
That is on purpose, the movie set up is like the mission briefing, we see details (like the acrobat, the pickpocket, the remote control guys, the con man playing the wealthy aristocrat, the guy supposed to create the power outage, etc), so we know all these capabilities exist on the team.
The heist scene itself seems implausible if we don't see them practicing at this stuff.
Remember Show don't Tell: We (the audience) is not told how all these puzzle pieces will fit together. When the heist is shown, it is surprising and delightful, but it all makes sense because we recognize how all those puzzle pieces now fit together, or when there is a worrying miss the team has to scramble to cover -- the acrobat gets injured! Can he still make his jump?!?
So keep this in mind, also. The mission briefing is not there to steal all the surprises and spectacle of the actual mission. It is to keep the audience from getting lost. In Ocean's Eleven the plan is so complex the audience needs an 80 minute "briefing" just to make all the skills involved plausible.
Short or long, that is what mission briefings are for, in fiction. Getting the audience ready to appreciate the ups and downs and roles of characters in the mission itself, when it is shown in action. You don't want your audience to get lost and confused, and lose their immersion in the story.
