If a balanced rod and reel combination is the goal, why add weight to the reel? It takes more weight to achieve the desired balance by using this method. Balance can be achieved with significantly less weight by removing or drilling out the rod's butt cap and inserting however much lead is needed to move the balance point to the desired location on your rod. The lead can be held in place with glue or wads torn from cotton balls, depending on whether you want to make the modification permanent or temporary.
I DID explain in my post above. Fortunately the question can be answered precisely, and the correct answer in such cases does not depend on anyone’s FEELINGS about what the answer should be.
I’ll give an actual example - on a typical 13-13.5 ft 8wt rod the center of mass in a balanced set up, and the point where you probably will want to grasp the rod is near the top of the upper handle. This is typically about 14” from the position of the reel in the down locking reel seat. The lower part of the lower handle is typically about 5” from the reel seat, or about 19” from the c.m. Let use an example that is close to the one I had, where I added about 3 oz to a 9 oz reel filled with backing etc. so it would be 12 oz, the weight of a reel plus backing etc. that balances the rod.
Let’s suppose we want to leave the lighter reel as is at 9 oz and instead add some lead at the end of the butt section to balance the torques about the c.m. The DEFINITION of balanced. The original balance torque about the c.m. (everything in oz and inch units) is 14” x 12 oz. The net torque for the new setup will be the torque due to the lighter reel 14” x 9 oz plus the torque due to the added butt weight 19” x B oz where B is the unknown butt weight, where we have assume all the weight is right at the end of the butt - best case senario. So 14 x 12 = 14 x 9 + 19 x B, or in other words the butt weight required to balance the lighter reel B = 2.2 oz.
In terms of total weight we have replaced something that weighs 12 oz with the weight of the lighter reel plus the added butt weight. So 9+2.2 = 11.2 oz for a grand total weight savings of 0.8 oz. On a 13.5’ 8wt that is IMHO a very minor difference to compensate for the effort, not a “significant” one, but of course you might disagree. “Well” you might say “it will also help the swing weight”, which is the moment of inertia, but still NO, as you have moved more weight further from the c.m. which has more, not less effect on the feel of the swing weight.
To make a long story short the total weight saving even under ideal circumstances is pretty minimal. But I admit that it would be a more attractive solution for people who can easily make the rod modifications themselves. It’s clearly a lot more work than adding weight to the reel. I added about 12oz of buckshot to the inside of the tip of my DIY wading staff, and it took quite a bit of volume and was not trivial getting it to not rattle. I use gorilla glue which expands as a “matrix” with mixed results. I’m STILL not too sure how it will do it next time.