Pin jaws are for small work and have several uses:
Used in expansion mode for internal holding within a dovetail recess. The dovetail is set away from the flat jaw surface by about 25mm. This gives you better access to the bottom of the bowl for easier tool work while your bowl is on the lathe.
The straight side can be used to hold the inside of a small box body.
In compression mode, they can grip a small part like a finial, or pen mandrel.
Jaw Travel Expanding - 30 - 80mm
Jaw Travel Contracting - 11 - 64mm