Generally speaking when you ask what a "properly balanced" outfit is the most common response will be that: with the reel on and loaded (backing +line) and the rod strung the balance point of the rod will fall within the grip, approximately where you will be grasping the rod. I disregard the notion that there isn't a balance point because "as you cast you have varying amounts of line out and therefore the balance point will be changing"; the act of casting involves intentionally applying a force to the rod to load and unload it to facilitate the cast. Rod balance is more of a static notion than a dynamic one, unless your outfit is way out of balance - then your arm and shoulder will tell you!

I have only had one outfit that IMHO was noticably out out of balance, it was a 7'-6" cane 4wt that I put a Hardy Featherweight on. The reel was far too light for the rod and the tip kept hitting the ground as I walked. Putting a heavier reel on balanced the outfit much better. Now there wasn't a significant difference in the castability, rather I no longer had to carry the rod by the blank to keep from digging the tip into the ground (really dodged a bullet there - whew)!