There are many ways to attach swim lines to your boat for self rescue, and the carriage of equipment for rescuing and unpinning other things.
Here's another offering on how to use long slings to attach swim lines to your boat, which then gives you the versatility of having a sling ready to attach as a belay system on the bank for rescues and safety cover.
My thoughts are this saves carrying specialist slings to attach your swim bags to your boat, and makes safety equipment easily accessible without having to rummage through equipment inside dry bags in the boat itself.
Anything that saves time, and saves faff in the event of an emergency is good in my book.