In reply to Pagan:
> Or climb the Diff to get out.
That might not be an option if he was on the wrong side of the "bad step" or unable/unwilling to untie and traverse unroped, possibly amid high seas.
I've seen beginners, particularly unfit or obese ones who after a few climbs would not have been able to pull themselves up a Swanage Diff (seem to remember it's still quite steep). Add wet holds (maybe the weather changed?) and a sometimes intimidating atmosphere and you have a need to hoist!