While configuring this module on the following page-

http://www.example.com/admin/settings/filters/defaults

The help lines at the top are-

Defaults only affect NEW content NOT existing content.
Place roles in order of precedence by dragging more important roles to the top.

I would like to suggest that these should be modified as -

Defaults only affect NEW content NOT existing content.
Place roles in order of precedence by dragging more important roles to the top.
This is used to determine what default a user will get when they have more than 1 role.

This is taken from module page documentation part. It is more clear now why the proper ordering of roles is important.
Thanks