Making a website accessible to as many people as possible is vital in capitalising on its potential reach. Ignoring a certain demographic, or designing a website to cater only for one specific target, can make or break a website in the long run.
Accessibility is more than just making sure your site works on different screen resolutions. Accessibility covers all sorts of issues, from designing for the colour blind and disabled, to making sure a site renders properly on PC & Mac, on different web browsers & computer configurations.
Best practices in web accessibility also improves your site in other areas, such as search engine optimization, which ensures your site ranks strongly in top search engines like Google, Yahoo & MSN.