They will keep your rotors and pads free-er from dust, road grime and water so they are nice and clean when required. ..and they'll last longer as a result too.
They may cause your pads to run slightly warmer, but personally I see this as a good thing as pads need to maintain temperature to work better anyway, -especially if you're using high performance pads with lots of metal in them.. Hi-perf pads are crap when they're cold.
Most of the cooling air is pulled from the hub through to the parimeter of the rotor anyway, so I see any additional cooling from their removal as insignifcant.
I think the OEs would have left them off if they weren't any advantage.