Mossback,

Doug emphasized the same thing w/my party in late June.  In fact I'll need  to stop at his place tomorrow and pick up another one as I'll be doing a 10 day solo. In my case, I suppose I might be throwing it to the other solo paddler traveling with me if he overturns.  He's so old he might easily just fall asleep on the water (wouldn't be the first time I've seen that happen).  Hmmm...  perhaps I should buy one for him, too. I ain't no spring chicken myself!

That's the only rationale I can think of as to why a solo paddler might need one.

Jimbo.  8-)