Hi Mauro, the grooved option will allow you to enter an additional distance which will then be used to form a kind of trench or groove around the inset border.

Here's the regular inset:



Here's with Grooved set and a small groove distance specified:




If you only check "Grooved" and do not enter any groove width at all, it will basically build a zero width groove with the inner area as a separate "plug" object.

Hope this helps!

- Michael