Mainly aero advantages and a bit of styling. Don't worry about the scaremongering, your LBS have to buy the spokes in tens (they buy normal spokes in much larger numbers) you can buy singles if you like.
A friend of mine ( 14st) rides a scott genius mc-10 with scott rims using bladed spokes ( not cheap) 2 sets. Every time we got a little agressive he would snap a spoke or two..three at afan. he got the wheels relaced using DT comp's and has never had a problem since.
Just our experience we found them a pain in the arse!