From CSS Discuss
Why use Cascading Style Sheets?
- By editing a single CSS file, you can make sitewide design changes in seconds.
- CSS lets you output to multiple formats quickly.
- CSS lets you use logical names for page elements. You can, for example, give a DIV the name "header", or a H1 the class "headline". It's self-describing.
- External CSS files are cached by browsers, improving load time.
- CSS eliminates the need for messy code -- namely font tags, spacer gifs and nested tables. This improves load time and makes developers' lives easier.
- CSS lets you do things normal HTML doesn't. Examples: better font control, absolute positioning, nifty borders.
- Practical use of CSS encourages proper HTML structure, which will improve accessibility and search engine placement.
- If you want valid XHTML Strict you have to use it anyway
Owen Briggs has a good self-described rant on this topic:
An interview with published CSS author, Christopher Schmitt, covers the Top 10 Reasons to Learn CSS.
A number of projects are dedicated to advocating these assertions (not confined solely to CSS):
- http://webstandards.org/ - A grassroots coalition fighting for standards that ensure simple, affordable access to web technologies for all.
- http://maccaws.com/ - Making A Commercial Case for Adopting Web Standards.
But see also What Css Needs