The primary purpose of bar end weights is to reduce vibration in the
bars. A set of bars without bar end weights has a very high resonant
frequency, and the vibration from the motor is easily transmitted
through the bars.
However, by adding the weight of bar-ends, the resonant frequency is
lowered, and the 'buzz' or vibration in the bar is reduced.
The secondary purpose of bar end weights is cosmetic, as you have
Google Cache of a discussion from the XS11 Motorcycle List about
vibration and bar end weights:
Original Link (not sure if the server is down, or my ISP is dodgy
motorcycle bar end weights Concours OR st1100
Also, I have owned both the Concours, known for the 'buzz' in the
grips and the ST1100.
I hope this helps you in your decision; if you need further
clarification, just ask!