There are many different types of hole punches. There are Rotary Punches that have five or six different size punches on them, and you turn the dial to use a different size. There is also spring punches where only one punch tube is installed, but it is changable. And not last but not least, the plain hole punch which is no more than a handle for the tubes to go in, or even a solid piece of steel that can only punch a particular size hole.
Holes in leather are needed for belts, as well as for hardware to go through (like rivets and snaps).
Besides punches for small round holes, there are oblong punches used for slots in an item, as well as slots for buckle tongues to go through.