It's a rare landing when I'm unable to stop the boat alongside so the the crew simply steps off and secures the boat. I think the danger in stepping off a moving boat is not so much in the leap as in the attempt to physically stop the boat, or to try to act as a human fender when things go awry.. This does, of course, depend on the boat's size and displacement.
But I reckon there have been plenty of turned ankles and other injuries to those attempting to 'jump' off the boat. (Imagine having to jump off something like a Hunter Passage 45 onto a low float!
Here's another thing that happens.. handing off the line to a "helpful" soul on the dock while still coasting, whereupon they promptly snub it down and send the stern shearing off away from the dock!!
When we do hand off lines we always let them know "We'll stop the boat"...