And on the flip side, computers can suggest beautiful theorems to mathematicians by making it easy to run virtual experiments.
There's now a burgeoning field of pure math called "Experimental Mathematics," where they do just that. A good intro on how computer experiments can be used in algebraic geometry is here: http://math.uga.edu/~noah/files/spheres.pdf
(Disclosure: Noah was my college roommate and we published a paper with Henry Cohn on experimental mathematics for high-dimensional sphere packing, so I'm a biased participant.)