This is really in the same spirit of the Agile Manifesto principle, “Individuals and interactions over processes and tools” and “Working software over comprehensive documentation.“
We hate documentation when it’s done in isolation, when it’s costly, when it means less discussion between team members. This is a point I make a lot when I speak to people about design. The goal should be to discuss ideas, make decisions based on discussion, and to favor discussion over huge decks of documentation.
A lot of people don't want to work with specs. I like to work with people to solve a problem, and in an iterative design, the point is to use sketching to figure out the design you're going to work on.
In a perfect world, we’d all have extra sensory perception and communicate telepathically what we imagine. But we don’t have that, so we rely on talking to each other, and explaining with pictures and models, doing what's necessary to find the idea that works—focus on talking to each other and getting to some consensus fast.