Originally Posted by TallRider

rotating weight hurts you more than non-rotating weight (particularly rotating weight that is far away from the axis of rotation - so mainly the tire and rim, and to a lesser extent, the spokes). the issues are:
a) for what type of riding does it hurt you?
b) how *much* does it hurt you?

The more you are accelerating and decelerating, the more rotating weight will hurt you. If you are doing a time trial on a relatively flat, non-technical course, you're doing very little accelerating after you initially get up to speed. Same is true for just-out-riding in the countryside in a relatively flat area.
If you are doing a lot of climbing, stopping and starting in traffic, or in an environment where you have to accelerate quickly to attack or cover someone else's attacks, rotating weight matters significantly. But for many types of riding it doesn't.