Steven Aquino has a wonderful article on TidBits about using Markdown as a visually impaired writer:
The less time I have to look at the screen, the better my eyes feel. Thus, what makes using Markdown so great is that I don’t have to waste time trying to locate buttons or menu options. I just glance down at my keyboard to ensure I’m pressing the right keys.
I couldn't agree any more. I'm pretty efficient with the tools I practice with. If I used a word processor all day, I'd probably be pretty efficient at using it too. But Markdown means I'm proficient at writing, not just using the tool.