Ensuring that the code that you write for your HTML and style sheet code complies with the standards is extremely important if you want to ensure that your page will display correctly in all browsers and be usable to those who for one reason or another do not use the same browser as you prefer [...]

Making your web site accessible to those with major disabilities, those with very minor disabilities, and even those who for one reason or another have selected to disable JavaScript or who don’t have a particular plugin installed is extremely important if you want your visitors to be able to get the greatest benefit out of [...]