Floating-thumb is an integral component of my right-hand technique. Not only do I use it as an anchor, but as many have mentioned, it acts as a lower-string mute.
Once I am playing on strings beyond the top string (B on 5-string, E on 4-string) my thumb lies down flat to mute the lower strings and just glides up and down.
When playing patterns on two adjacent strings, the thumb mute timing is critical. The left hand can act as a mute for the upper string, but the thumb must open up to allow the lower note in the string pair to sound, but then mute simultaneously as the upper string note is struck. Coordinating this action becomes more difficult as speed requirements for a particular lick increase.
I guess if it were an easy technique there wouldn't be such wide and varied discussion on the topic. And because each player is unique and applies his own custom-crafted method, there's no right or wrong. The bottom line is it takes a lot of practice to use it to its fullest extent.