Wrote a mandelbrot generator for uni that performs at several fps on a 25MHz clock using 8 multipliers. Definitely not possible on a CPU! https://instagram.com/p/2Y4CMtP95Q/?taken-by=yawn_brendan

But yeah pretty much any repetitive computation. 3DES enc/decryption is another example (although I think people normally use ASICs for that when they want to do loads of it).