I want to add one thing. Part of the re-machining functionality is re-roughing. What this does is allow you to start with your largest cutter, rough as much as that will allow you. Then go to a smaller cutter, and madCAM will automatically find the areas that the larger cutter couldn't reach. Yes, I suppose with enough effort and time you could do this manually, but who has that kind of time?? And if you make a mistake and miss an area, you are probably going to do some damage. In my opinion, if you do 3D work, the re-machining will easily pay for itself.
This may sound like a repeat of Sven's comment, but I wanted to specifically relate this to roughing.
Dan
(Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)