Not a WC person, but blitzing means chaining attacks together one after another, generally moving forward, forcing your opponent to retreat and hopefully overwhelming him.
The pros are that a good blitzer can be very difficult to defend against, especially if you're inexperienced. The constant attacks can make the opponent forget about countering since he's too busy getting out of the way, blocking, etc.
The con to blitzing is that it tends to be quite linear, and while blitzing, the attacker generally can't defend himself from a well-timed counter. The best strategy against blitzers is to get off the line of the attack and counter as they're coming in.
Both strategies (blitzing and countering the blitz) can be very effective, and it often comes down to the relative experience and intensity of the competitors.