can do something that nothing else can do

They can pick up and drop off anywhere

Igor Sikorsky's design is being used for the following:

Rescue work
The Sikorsky company is still building rescue helicopters today, big rescue helicopters
The first Sikorsky rescue helicopter could only pick up 1 person, but this fenomal powerful monster has room for 32 these days
It can search in the dark by an infrared camera in the nose which is connected to a monitor. And it show exactly where the person is by zooming in to the exact place till the face of a person can be spotted
To carry massive machinery to places which have no access whatsoever

Frank Pierre Piaskecki's design is being used for the following:

This helicopters dominated the heavy lift market ever since its being designed
World’s most employed heavy lift helicopters
Enter service in 1960’s in Vietnam. Over 2000 are still flying. They're the heavy lift workhorses, carry huge cargos of men and equipment to places where no otner machine can reach and it can carry several cargo’s all at once
Perfect for a battlefield role where a single helicopter often needs to deliver separate loads to different units in one trip. Designed with one thing in mind – heavy lift