In the module's navigation, you'll notice a menu item titled "Shared Characteristics". The purpose of this page is to allow direct mapping of field settings between field types, to provide a little meta data to the Core script. A little explanation may be necessary!
With the addition of the customizable field types, the field type settings became totally discrete entities, semantically distinct from one another. In Form Tools 2.0.x, the Core code was hardcoded: it would know that the field storing the Option List for radios and for checkboxes were the same. But this changed in 2.1.0. So, for example, if a Form Tools administrator using Form Tools 2.0.x changed the field type of a dropdown to a multi-select dropdown, they wouldn't need to re-specify the Option List being used. However, in 2.1.x, it's not so simple.
This page was the solution: it lets you map arbitrary characteristics of your field type settings so that changing the field type will still maintain as many of the settings already specified. Fundamentally, it allows for a more intuitive interface, intelligently retaining as many configured settings as is possible, depending on the source and destination field types.