Old carpenter I worked for had one. You get the solid jaw near the head of a nail then slide the handle down to make the jaws close.
There are times when the nail head is flush or below flush and you need to remove it - then use this tool. It’s going to remove a chunk of wood, so not something to use on finish or trim carpentry.
My dad had one of those. Used it a BUNCH as a kid. I will put one bitchin’ pinch on your index finger if you use it just wrong.
My brothers and i were very familiar with that thing and were able to pull lots of nails that a claw hammer or pry bar would never reach.