In terms of a broad population, I am not sure there is a meaningful difference, though. You can iterate on your ideas on the whiteboard or you can iterate on your ideas in code, but the intent is the same. Either way you are going to throw it all away once you have settled on what should be the final iteration anyhow.

It just comes down to where you are most comfortable expressing your ideas. Some like the visuals of a diagram, others are more comfortable thinking in code, some prefer to write it out in plain English, and I'm sure others carry out the process in other ways. But at the end of the day it is all the same.