Separation of layout and content allows you to do things like this: http://www.csszengarden.com

A few benefits that may be worth the headaches of floating divs:

* Redesign your pages without ever touching HTML (mobile/tv version)

* Improved SEO by arranging important content up top

* (Generally) lighter page sizes because CSS is in external file being cached

But I actually use floating divs because I find them easier. Tables are easy too, but after years of hacking on broken CSS--most of the thorns have faded away for me. YMMV. Use what works best.