I saw this thread about VFR bars and the weights to go in them.

Are the weights necessary? Can I install them after installing the bars themselves?

You don't need the weights and they can go on anytime. Have to remove the grips though if you have to put in the inserts.

The weights are to quell engine vibration, if it's smooth enough for you without, don't bother. They may also help in a wreck though to keep from bending and breaking levers.