Yes it is. So many Cosworth's out there with Idle that hunts up and down or revs its nuts off cold because the mapping is garbage its unbelievable and one of the things that has given the YB scene a bad name as outsiders looking in just see these horrid smelly old Sierras and escorts that don't even idle when cold or the owner cant drive unless its flat out because they hesitate and jerk.

Making one fast is child's play and anyone with a little mapping skill can get reasonable results. Making one drive properly and return decent fuel efficiency is where the skill comes in.

Its also of critical importance that people understand this:
Those with no understanding of an engines needs will almost never get a car to drive right or be efficient, especially when cold. Laptop skills do not enable you to map.