`draw_shadows` effects the shadow cast by the Sublime "minimap" -- the code shape outline on the right side of the window.

You can see the effect of turning it off by comparing the right sides of the single pair of (before/after) screenshots in the article.

before: http://thume.ca/assets/postassets/sublimesecrets/debug_rende...

after: http://thume.ca/assets/postassets/sublimesecrets/configs.png