Advantages of CSS over Presentational Markup

Web pages can be styled using presentational markup (HTML) or CSS (Cascading Style Sheets). Styling using presentational markup is "old school" and has a number of disadvantages. CSS is, technically, the "right" way of styling web pages because (X)HTML is a structural markup language.
Disadvantages of presentational markup:

• Leads to large, bloated web pages
• Makes the code of the web page extremely complex
• Each element has to be styled individually
• The rendering of the web page is slow
• Lack of flexibility - once done, no easy way of changing the design
• Poor accessibility - makes the page less accessible to the blind
• Results in low search engine rankings

Advantages of CSS

• Web pages contain only structural markup, therefore small and fast to load
• Keeps the code of the web page simple
• A single element can be styled using a single CSS rule no matter how many times they occur
• Page is rendered quickly
• Design can be easily changed later
• Page is accessible to disabled people
• Results in higher search engine rankings