Why avoiding tables for layout is important
Tables are slow
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In almost every browser out there, unless table widths are specified explicitly, all the text in the table needs to be rendered before the browser can figure out how wide to make the various table cells. This means that pages load slowly. Note that using CSS for layout doesn’t necessarily help here, since there’s the same problem if the widths aren’t specified explicity.
Tables can be inflexible
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One of the common tricks to make tables load more quickly is to specify the widths for all the table columns. This means that the table renders pretty quickly, and the user can see your text right away. The problem is that you’ve just specified the width for the page. Again, note that you can have this exact same problem with CSS if you specify all the widths explicitly.
Accessibility issues are easier with CSS
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Tables also mean you have to present the information in the same order you want it displayed. You have to present data in the left column before the columns to the right. Using CSS for layout, you can present the data in a logical order and use CSS to control the appearance. For example, in a three-column layout using tables, you’ll see left-column then center column then right column in that order. Using CSS, you can put whichever of the three columns is most important first, and keep the layout separate (which is the whole point of CSS).
Tables don’t degrade
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The most important reason why using tables for layout is that they don’t degrade gracefully. You may often seen some websites which is not adjusting its width based on the browser width.
Tables don’t print as well
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A huge problem with tables is that they don’t print terribly well. With CSS, you can use a print style sheet to give another look to the page. This style sheet can also include page-breaks that are under your control. You can also have elements that only show up when rendered to a screen, but not to a printer (headers and footers, for example). Or elements that show up when printed, but not to a screen (useful for expanding links so they’re visible when printed).
Tables have some advantages to – for example, its easier. And more compatible across browsers.