Floating Floor??

I am getting ready to install a cork plank floating floor. The manufacturer says to leave a 3/8 gap around the edges, but then I read on this site that its not critical an 1/8 is good. I also watched a video with 2 pros installing a cork floor in an empty airstream, lay down the vapor barrier, leave a space around the edges,trim mouldings and done. Now, how does that floor float when everything is installed back on it, somebody please enlighten me here!!!