Visualise something like an egg carton, all peaks and valleys.
If you had already cut the entire 2" deep mold with a 1/2" diameter ballnose and then you wanted to recut just the top 1" of it over again because, say they had cropped the top 3/4" of the model, and reskinned it (its not just a flat plane top, but is 3d), then you would want to save time by not going all the way down to the bottom any more, but would just want to rapid across the open areas until you get to the islands (this is finish cut only), start at 1" depth and come back up and mill the detail on the island plateau. Am I getting close to making myself clear yet?
