I have to go with Ray on this one (reply #2). When I think of the problem with weight balancing, I have to fall back on what I do for a living. As a motorcycle technician, this means wheel balancing. I've seen wheels with weight on one part of the wheel, placed there to counter weight placed on another part of the wheel. I've taken a couple of ounces off of an improperly balanced wheel. But one of the things that occurs most often is not mounting the tire correctly to begin with. There's a heavy side that must be placed opposite the tire valve.
With that being said: "Choking up" on the handle to "balance" the rod in your hand might be a better alternative to adding weight. As they make the rods lighter and lighter, we notice the weight differences easier. We start compensating for things we just didn't notice until the rod's weight is back up to the older heavier rods.