i DO get what they are... but explain something to me first, please:
besides just the designer wanting more content above the "fold", the purpose is for what? handheld computers?
if so, the screens usually aren't 800x600 or up are they? ive never seen one, and imagine them to hold about half that or a significantly smaller resolution... ?
so if they are really small resolutions, then i see why fixed layouts are bad... but if they are bad, then why do a lot of people use fixed column sizes with their liquid layouts? wouldn't that rather defy the point?