Well, LGM, I guess I respect your disagreement but just as respectfully also disagree with you.
Unless you're using a truly tiny bit for carving (less than 1/16"), then my experience is that z-level roughing gets rid of enough material to allow for carving, and usually does it faster than 3d raster roughing, when you use appropriate feeds, speeds and stepovers. The "shallow" stepdown on each z-level pass is, frankly, relative and with large stepovers, as Gary recommends, irrelevant in terms of machining time.
I would be uncomfortable going the other way in most of the materials I cut -- shoving a large bit deep into a piece of hardwood. It's hard on the spindle, hard on the bit, and risks yanking the material out of whatever work holding system you're using. Granted, in a foam material this is not so much of an issue. If the carving is, in fact, shallow and I'm using a 1/16" or 1/8" tapered ballnose carving bit, I'll probably skip the roughing step anyway, and would be tempted to skip it in foam.
As I stated before, I've never before tried to shove the roughing tool deep enough in the material to get that error message. Most of the time my roughing passes take a few minutes at most. If you're uncomfortable with that, then Aspire gives you other choices.
D&S Artistic Woodworking http://www.dsartisticwood.com