With the cMP one could buy a lesser configuration and then upgrade it as their needs grow. With the nMP, and most of Apples computer lineup, one has to guestimate their future requirements and buy a system capable of meeting those needs as they won't have the option to grow into them.EDIT:
That being said. And this is serious if you don't have an absolute reason to put this machine to work for at least 50% of it's capability, then this Computer is A WASTE. I mean to me, I look the model I want and it's $6,099, which I would love to get. But I don't have an immediate workload for that monster, so that would be such a waste, compared to having a SECURE MacBook/MacMini Future, consisting of 2 MacBook Pro 15" purchased at the proper moment every 5 years (black friday-ish etc) for $1799, and then 2 MacMini's for $1099 each, purchased right when they came out, those machines would be a complete eco system containment center for 10 years also) So yeah if you don't have anything but TOY USAGE, it's a waste. But a Marvel of a computer!
BTW, I don't consider the Mac Pro to be a monster. IMO it's a middle of the line workstation easily out classed by something like a Z640 or Z840 system. By Macintosh standards it's a monster. By market standards it's so-so.