On a Hobie 16, the problem arises in strong wind, shallow water, and a muddy bottom, where strong wind pressure against the bottom of the tramp can quickly drive a non-floating mast head into the soft muddy bottom, before you have a chance to right the boat, especially if you are alone, or have an inexperienced crew member-- at that point, it is impossible to extricate without the help of a powered vessel or a winch from shore, if you are close enough to shore... "Sealed" masts often aren't very watertight, and they sink pretty fast if you can't right the boat immediately. The pressure on the bottom of the tramp and the resistance of the mainsail to the direction of motion of the capsized boat as it is pushed across the surface operate to force the mast head down even faster, even when mainsail and jib are fully released. Some kind of a float might make sense if you are sailing in these special conditions...