I'm a software developer and I always find that grabbing a whiteboard and drawing diagrams or other such information is very useful when trying to agree on a solution (or even agree on the problem). I work remotely and very rarely see the rest of my team in person, so the clear benefit (to me at least) of in-person whiteboarding in those situations is very stark.
Yes, you could probably accomplish the same thing by writing up a proposal spec document (which you'll need to do eventually) but the downside of doing that during the drafting stage is that it lengthens the feedback loop and not everyone will read such a document thoroughly and leave a thorough review. In-person whiteboarding is usually much faster and everyone in the room is almost always on the same page.
Yes, you could probably accomplish the same thing by writing up a proposal spec document (which you'll need to do eventually) but the downside of doing that during the drafting stage is that it lengthens the feedback loop and not everyone will read such a document thoroughly and leave a thorough review. In-person whiteboarding is usually much faster and everyone in the room is almost always on the same page.