How to keep a sketchbook, and why! In this Urban Sketchers Chicago blog post by Barbara Weeks, the benefits include the expected, such as developing your drawing skills and capturing fleeting ideas, and also things you might not think of:

“5. Cheaper than a psychiatrist
This reason may be my own little reason but I share it with you. Waiting used to be a time of aggravation and annoyance for me. Now, I think, “Oh good I can sketch.” I also have more sketches done in hospital emergency rooms than I care to think about  but they kept me calm and sane. And sometimes when I’m “in the zone” it’s like meditation.”

Read more at Urban Sketchers Chicago: Every Visual Creative Should Keep a Sketchbook.