I recently read Molly Inglish's article on the Whiteboard Design Challenges done at Tradecraft. I perceived the 20-minute exercise as an effective means of fleshing out a product concept or a design solution quickly.
I chose to test the technique out on Early, the alarm clock app I began to dream up a few months ago. Perhaps this exercise was a chance to resurrect and refresh the idea:
Annotating the sketches was an effective way to track thinking while maintaining brevity in the process.
Surprisingly, the exercise propelled me to sketch out wireframes right off the bat: