Even in this age of cell phone cameras, artists sometimes carry sketchbooks for those times inspiration strikes. After all, a camera can't suggest how to portray a view; it only shows what's there. If you don't recall what attracted you to the scene, you may wonder why you took the photo to begin with.
Writers aren't known for jotting dialog as it occurs, but it's a good idea to get it down asap. Otherwise, when the time comes to use it, you might reach up there and grab empty air. Bummeracious. With the 'sketchbook' method of saving inspired dialog, you don't need fussy prose--just who says what, along with some stage cues. A second benefit (sort of like the 'character interview') is testing encounters between characters. If they act bored, then find another foil for the current POV. Often you'll only need to remember a joke or amusing incident, though dramatic conversations can go several pages. Things will change by the time you're ready to use it in the story, but it's invaluable to have these talking points saved. Thirdly, you'll already have a first draft of the talk. By the time it's needed, you'll see better ways of doing it. A short example follows.
From the Satire Zone
Rick and Jake are two construction workers on a break, proving that it isn't all sports and women. A surprising range of topics comes up, from erudite to goofy speculation.
RICK What would you say is the single most-used word in World War 2? Forget 'sir' and 'heil'.
JAKE [Ponders] I'd go with 'halt', since both sides used it.
RICK Could be. The allies tacked on 'who goes there', which in German is 'ist da jemand', or 'is anybody there'. Which of course is less effective, because all you have to do is answer 'no'.
JAKE [Laughs] Like on Hogan's Heroes!
The subtlety of the joke might have been lost if we only remember it was vaguely about World War Two. Dramatic scenes may need more stage cues, and even notes when ideas for future scenes occur. It's just another way the cast can show you which way they want to go.