If you're specifying @screen as the Media Type, the primary reason I can think of for going back to floats is art direction - especially if you wanted to float images alongside a block of text. I know there are "better" methods in more modern versions of the spec, but this is one that still seems to get a fair bit of use.

Old CSS never dies, it just goes to live on a very special farm upstate where it only has to do 1 or 2 jobs.