In my limited understanding, the ballast resistor is used when the flasher unit is the older bi-metal type that is dependent upon the internal resistance of the incandescent bulbs. When you add LED bulbs, they have a much lower resistance and the flasher rate is radically changed without adding resistance.
just my 2cents. i bought a ted porter Ei LED taillight unit for my r100gs and its great. the running light position is a little bright but the brake light is still MUCH brighter. people stay back more now.