What is a round knife used for?

There are many varieties of round knives, they can be called Rotary knives or circular for certain knives, but there is more, I have listed some sites:

* http://www.appliedcutting.com/?gclid=CLCD6uDY4JUCFR8SQQodKQvNXw* http://www.tandyleatherfactory.co.uk/pc-70843-205-osborne-70-round-knife.aspx* http://www.patentstorm.us/patents/6327783/description.html