Big Iron is good at both. But a lot of the cost of Big Iron goes into the networking, so to put Big Iron to work on Shrek is a waste of a lot of expensive networking equipment. So they're generally not used this way. Big Iron really shines in problems analogous to the Billiard Balls (like modeling the weather or how air flows around a jet fighter's wings, or how far a nuclear mushroom cloud will billow given the winds.)
Grid Computers are very good for problems like Shrek, but not so good for Billiard Ball type problems simply because the worst computer on a grid computer is usually pretty bad and nodes on a grid fail often so there's lots of waiting and lots of redos.
FlashMob computers have an advantage over Big Iron in that they are inexpensive and an advantage over grid computers in that they can solve Billiard Ball type problems. Unlike big iron, FlashMob computers can be sized to fit the problem at hand by adding more or fewer nodes. FlashMob Computing nodes are also dedicated to the problem at hand, so individual nodes are much more reliable than grid computer nodes.
Amazing and the ramifications are dramatic, namely that the barriers to entry for tackling supercomputer- related questions are greatly reduced.
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