In rec.boats.paddle Larry C wrote:

a dynamic line like poly is fine for a throwrope to recover swimmers
since it has a bit of give when that 200 lb boater and kayak full of
water hits the end of the line, but since we normally don't have the
option to carrying two ropes, you are better of using a static line
that can double for your mechanical advantage systems. If you are
trying to pull a boat off the a rock while on a steep river bank, the
less stretch you have the better.

The only thing I have to add is that nylon climbing rope, polyester
rappel rope, or Kevlar stranded rope (I've seen it) are all terrible
as a throwline, because they sink.

It was enervating once watching a swimmer unable to grab a sinking line,
then wash over a waterfalls. Fortunately he was only mildly injured.

I won't divulge who had the idea of putting Kevlar rope in a throwbag.
It was for strength I guess, in the days before Spectra.