tl;dr: The author filed down the sharp edges of their M4 MacBook Air because the corners dug uncomfortably into their wrists when using it on their lap. They used a metal file and progressive sandpaper (up to 1200 grit) with tape as guides, applying soapy water to contain dust, and treated the trackpad/keyboard areas with tape to prevent debris intrusion. They frame it as a reminder that laptops are tools and worth modifying for better ergonomics.