Since I only play DDR at arcades, the obvious con is that I easily spend $10-15 a month playing it (not to mention another few bucks playing other games during my "down time"). And the arcade mixes don't update that frequently, so even with 300+ songs to choose from one will eventually get bored with it.
The pro, asides from the vigorous workout, is probably being able to pick up beats and music rhythms, which I guess can make you a better dancer -- as long as you're not trying to step on pretend arrows in a club.