Everybody says avoid tables when you are creating design elements like layouts, themes, pages... Why?
(X)HTML says; tables are for tabular data not for website-layout
Tables have much design code than content, divs are faster for download. Save bandwidth!
Tables let confusing while creating layout(You have to remember which TR or TD ends in which template file)
Debug is easier with CSS, mostly all design code is in one css file
Change design anytime just using css-style files without need to touch template files
With CSS you can separate design from code.
Most CMS support cache for CSS. Less work for server-cpu and more speed for visitors.
Printing pages in css-layout are easier than pages with tables
Absolute or fixed positioning is not avaliable for table-cells.
With tables you cannot set priority of content. (Browsers scan from top to bottom)
Disabled people who surf with help of special devices cannot get the content of pages with tables in the right order.