The type of corkscrew with two “wings” only pulls the cork up part way. Some corks are so tight in the bottle that it’s hard to remove the partially-pulled cork.
After the initial pull, this handy little device sits on top of the bottle, “hugs” the cork, and provides a new, elevated surface for the mechanical puller to act upon. The net result is an easy way to pull the cork another 3/4 inch further out of the bottle.