The benefit of parelle layout is more obvious for 5 columns layout. 4 pair of extra wrapper divs are removed in the nested design. So are the relevant CSS codes.
It's indeed rare to use 5 columns as page layout. But this design can be used to design in-page 5 column data instead of tables. It can be used as a creator for tableless table.
If you like liquid layout, set the unit to % . For fixed width column, set it to px or em. Be careful to use em coz em layout is relevant to the font-size defined in body tag.
Normally, you don't have to set height values. The height of the columns will extend with the content. Of course, it's an easy thing to set the height.