All canoes in our club carried a throw bag on day trips, but I have never seen anyone use one. And we paddled gnarly, boulder-filled rapids pretty much year-round in the Vancouver area. To use a throw bag would require that lead boats eddy out, and the paddlers stand on shore, waiting for the distant, trailing boats to arrive, all the while hoping for or expecting a capsize. No one would do that, other than for sport, such as the end of the infamous Adams Canyon, in which up to 40% of the boats usually capsized, floating out into a large eddy. Otherwise, If the leading boats eddied out in a calm eddy, then a capsized boat would self rescue. On most of our rivers, calm eddies., in long rapids, didn’t exist. Canoe-over-canoe rescue was the most common technique, in Class 3 rapids, usually multiple times per day. Most paddlers rarely capsized in Class 1 or 2, unles they were surfing a wave.
That being said, Kathleen and I have often used our throw bag on our northern Canada wilderness trips. The bags make great clothes lines. We have also used the bag as an extended bow line, to secure our canoe to a boulder or tree, while on shore. We usually trip alone, which means there is no one to throw the bag to. But we always take it. It’s a rule, and clothes lines are convenient.