Some people say that the weights reduce vibration. I've never had a problem with vibration, so <shrug>.
From first hand experience. I removed my barend weights for mounting my barend mirrors on my stock bars... didn't notice much until my hands started going numb... mirrors shook like mad too... When i switched rizoma grips, i had some room to mount my mirrors onto the bars... and was able to put my barend weights back on. Made a pretty significant impact on the vibration in the mirrors... Not sure if the weights did it, or if changing mounting points did it though... /shrug for me too...