Ostensibly, they did this to advance human knowledge of science. But let's be serious: the made their saw blade mostly because a saw of shark teeth would be totally awesome.
But awesomeness alone does not get you published in the scholarly world. So when K. Korn, J. Brash, S. Farina, and A. Summers presented their findings at this year's meeting of the Society for Integrative and Comparative Biology, they claimed to be studying the means by which shark teeth cut:
Shark teeth both pierce and cut their prey, which is viscoelastic and structurally and materially heterogeneous. We propose a device for testing the function of shark teeth in a biologically relevant context with respect to their movement relative to the prey. We used this device to test whether tooth shape has an effect on cutting efficiency on a large actinopterygian prey item (salmon) and how quickly teeth dull. Teeth from four sharks, tiger (Galeocerdo cuvier), sandbar (Carcharhinus plumbeus), silky (C. falciformis), and sixgill (Hexanchus griseus), were attached to 30.5cm straight saw blades with epoxy. Each blade was mounted in a reciprocating saw and applied to a chum salmon with constant force.
As you can see, it's quite effective. The builders call it the Jawsall, which is sadly a one-off product that is not available for the consumer market . . . yet.