Another example, here you can see how Inset is able to work off of more generic shapes like a curved surface:





That's another kind of thing that wouldn't work if it tried to do just a straight single-direction extrusion from the originating surface instead of using a surface offset of the originating surface with offsets of the surrounding pieces to cut it.

Some other interesting variations on this one - here with grooved enabled:



Here with grooved + expand - kind of puts a piping around the outside edge as a separate solid:



- Michael