In the Guild Wars 2 previews I was intrigued by the Sink and Float mechanics as a means to control underwater battles. However, I've not seen it much in the released game (in PvE, at least, which I play mostly). My thief has no relevant abilities that I know of but the official wiki list of Sink/Float skills isn't long so it appears to be fairly unimportant.
The only useful effect I could think of off the top of my head is preventing a human opponent in PvP/WvW from getting to the surface when they're drowning, which is the only application mentioned on the wiki as well.
Is this effect worth the effort? Does Float have similar applications against water-breathers (e.g. force a shark to the surface to prevent it from breathing)?