En Route Sum-Up

When the Five-Man Band (or similar team) has a new mission in store, the Mission Control or an equivalent character (The Hero, The Smart Guy) will almost always explain the situation on the way, not beforehand.

This En Route Sum-Up will often include the entire relevant Backstory of the location or characters that the team will encounter, as well as an outline of the planned course of action. Common statements that prompt it are "Let Me Get This Straight...", "Wait a minute", or a Postponed Questions. Just as often, though, the scene will simply open with the description.

Narrative reasons for this:

Traveling in the Cool Car, or simply walking, makes for a more interesting background visual than standing around a table in the Home Base. Just as the crew is obligated to Never Give the Captain a Straight Answer, so too must The Captain wait until a narrative-appropriate time to tell the crew what's going on.
The mission may be so urgent that there's No Time to Explain beforehand.

During this talk, characters may be seen suiting up and otherwise preparing, despite their presumably not yet knowing the exact nature of the mission. This can lead to some Fridge Logic… what did The Hero say in order to get everyone to go? Also, did she consider whether a member of her not-yet-informed team just might have, in storage, a handy tool for this particular job (which would be inconvenient to go back for)?

This can be outright perplexing if one of the in-the-dark characters is the vehicle's driver (or pilot), given that he presumably doesn't yet know the destination. (Does the team follow some traditional "pre-route", such as a circle around the block, before "really" embarking?).

This is a common practice for the duo at the center of a Crime and Punishment Series or Buddy Cop Show.

Examples of En Route Sum-Up include:

Film

Transformers: Revenge of the Fallen has Major Lennox explain NEST's cover story in Shanghai moments before the team touches down.

Live-Action TV

In Criminal Minds, while the team are alerted beforehand where the next crime is, they almost always cover the backstory during the plane ride (unless its local).
This has been done in House in various ways. On occasion, it is not noted what the MRI of Doom is being used for until it is already in use.
This has been done on foot in The West Wing and Studio 60 on the Sunset Strip. Characters frequently discuss sensitive situations in the hallways.

Video Games

In Call of Duty: Black Ops, the beginning of the Khe Sanh mission is Woods explaining to Mason how MAC-V-SOG was formed.