As a web designer you give each use case a name and a backstory. You imagine what users do not only on your website but the rest of the time too. That makes them more interesting cases for your clients to consider. The genius of this book is to suggest personas with typical hearing, vision, cognition and mobility challenges. How typical? I've had only one legally blind co-worker, but it's pretty common for me to see everyone at the conference table staring back behind thick glasses. The difference is only in degree, and to my mind the extreme cases are the most helpful in thinking through an issue. SEO helps everyone, but especially the googlebot. Not everyone reading my website is going to be impaired, but on Friday night, who knows? (Come on. You read the message boards.) So here's a primer on accessibility issues that gives you a way of thinking more broadly about good design. Feel free to dial down what you share with your project team. Your audience may be simply hurried or distracted. Just the same, if GrubHub doesn't include a drunken-diner persona on its web projects, it's missing a bet.