A:
Well duh they are for Suckers of course.
Hey sorry couldn't resist.
Researched this and decided it is used as a Hook that Rides ON your Live bait Fish.
So, your Bait is a Fish that is NOT meant to be dead or die. You rig him up so it stays on your line and this Hook (Sucker Hook) is a Trap like Hook that releases from the bait to catch the Target Fish.
I Could be off a bit.