For the last couple of years or so, web designers have been moving from the traditional table based format for designing websites, to CSS (cascading style sheets), so why is this?
Page Load Speed
Having an external CSS, much of the code is contained on a page other than the one being viewed, this can make quite a dramatic difference to the volume of code on each page, often cutting it by as much as half. This means the pages will load much faster, therefore providing a better experience for the site user, but also helping with SEO, as Google’s algorithm now includes site speed. Of course, if you use a CMS software such as WordPress for blogging, this is all taken care of automatically anyway.
Easier Site Redesign
With a traditional table based website, if you want to redesign it, you have to update each and every page. However because a CSS based site contains all the design information on the style sheet and the website content on the pages, you only need to update the CSS, the design will then be applied to all pages which reference it. The big benefit to the site owner is that reduced time = reduced costs.
Reduced Margin for Error
Imagine re coding lots of pages, possibly hundreds, or even thousands, nobody is perfect, so the chances are there will be a few minor errors here and there. With CSS as long as you get the one referenced style sheet right, all pages will be correct.
Improved Search Engine Optimisation
There are a number of ways that the coding on your website can aid your SEO efforts. Firstly by having a smaller page size, they will load faster (as mentioned before, Google like that). Less code means a higher ratio of content to code, again this is rumored to help SEO, and finally a consistent structure to pages, with correct use of h1, h2, h3 tags on all pages will also help emphasize your keywords to the search engines.
There are probably other benefits too, so if you can think of them please let me know, I will update the article accordingly.