I would guess they just did this for the contest $ and fun, but prime numbers do have practical uses. I know they use them in cryptography, also computer coding stuff?
This number isn't practical to use in any type of cryptography (or legal in USA) but shorter ones are used for stuff like encrypting govt. systems and keeping your online transactions secure. Also, primes were what cracked the Enigma code.
At this point we don't actually know how this type of prime numbers work- there isn't any formula to find out the next one as far as I know. I expect the more #s they find though, the closer they are to figuring out the formula, which could actually be useful. When they figured out other formulas for different set of primes there were lots of practical uses.
But basically, this discovery is not useful at this point really, just fun for math geeks and a little cash for the math dept. at UCLA. It doesn't take much more than an internet connection to enter this contest though, barely any money or man power or brains. You just download a little program and let it run in the background, anyone with a computer can do it.