GridLayout provides absolute positioning for controls placed on the page. Developers that have their roots in rich-client development environments like Visual Basic will find
it easier to develop their pages using absolute positioning, because they can place items exactly where they want them. On the other hand, FlowLayout positions items down the page like traditional HTML. Experienced Web developers favor this approach because it results in pages that are compatible with a wider range of browsers.
If you look in to the HTML code created by absolute positioning you can notice lot of DIV tags. While in Flow layout you can see more of using HTML table to position elements which is compatible with wide range of browsers.