This is an issue that has plagued me for a long time. If you are trying to create an inlay by making a "pocket" and a insert, you cannot just cut the insert as "Outline, outside" and the pocket as "Fill". There are two reasons:
Sharp corners: The parts of a design that are inaccessible because of bit size are not the same between the pocket and the insert. In fact, they are the exact opposite. So a new design has to be created that compensates for both the inside and outside sharp corners.
Fit tolerance: Even if your design had no sharp edges, it still would not be good to cut the two parts to the exact same dimensions. Depending on the material, you'll need to leave some space between the parts so that they can fit together.
This new app takes a design (you have to have your shape selected) and creates two new shapes: an "Outline" shape that is the cutout insert, and a "Fill" shape that is your pocket. You can then use these two shapes in your designs (and get rid of the original).
Give it a try and let me know how it works for you! The exact tolerance you should use depends a lot on the type of material you are using, so you may need to experiment.