Not calling anyone out because I have valued and enjoyed all of this discussion, but I do encourage some thought on this if you are still struggling. I noticed something here that a few folks are missing and it is critical.
When one loads a loader, or forks, or a grapple - that weight/force is not being placed directly in front of the axle like in the case of a snow plow on a truck. The loader connection points to the tractor are typically located closer to the operator station and thus the forces are distributed to both the rear and front axles through the tractor frame. It is the distance to fulcrum where the force acts that is important here. One can still load the bucket sufficiently to "unload" the unweighted rear, but point is you are not placing and distributing the force directly at and beyond the front of the front axle.
This concept allows fun center of gravity toys like this to function.
So - adding 1,000 pounds on your 3pt can easily and fully counter balance a full 1,000+ pounds in your loader due to where the forces are actually acting. In this case your loader force is always acting behind your front axle, and if the load is extended far enough forward, or heavy enough to push the center of gravity past the front axle, then it will tip up. (That would be the case where someone pushed down on the eagles wings and your finger is the center of gravity/front axle).
That tipping forward will never happen if you have proper counter balance beyond the rear axle, AND your operating front axle loads will be at or below a fully unloaded tractor scenario. Having counterweights protrude past the rear wheels is a little bit of a pain for agility, but placing just 500-1,000+ pounds a good distance outward of the rear axle will let you do wheelies all day with a completely full loader and a football team hanging off the loader. This is why I sometimes use a heavy duty cutter for counter weight as it places some of the weight at a greater distance and provides a greater force/moment acting on the rear axle fulcrum which in turn
helps reduce the loading on the front axle in all circumstances.
To help with the wheels on ground vs lifted issue, think about the split second before your rear wheels lift off the ground. At the point, all four tires are still in contact and yet the force on your front axle is almost at its maximum stress. If you placed your pinkie finger on the loader bucket and pressed down, then the rear wheels would lift off the ground. The difference in force on front axle in those two scenarios is negligible. The force progression is continuous and nothing special happens when the rear wheels finally come off the ground. The force on the rear axle simply goes from one pound to zero pounds...
Conclusions:
1) Counter balance weight at almost any distance behind the rear axle can and will offset similar weights/forces added to the frame of the tractor and thereby front axle when using a loader. More weight, and or greater distance from the rear axle will amplify the effects of lightening the front axle load. The impacts are far greater than just a nominal 10% or so mentioned earlier since the loader is imparting its forces towards the middle of the tractor which is not too terribly much farther from the rear axle than are the ends of your three point hitch and added counter weights. (Box Blade, Cutter, etc...)
2) Center of gravity is important to understand as well as fulcrums and force amplifiers. (Distance from fulcrum, etc...) Front end loaders are designed to place the actual working forces as close to the CG as possible, but moving them up or down can change the situation drastically in seconds. This is why counter balance rear of the rear axle is so effective at correcting problems associated with overloaded front axles.
3) Perhaps your front axle might not break of wear out right away if not using proper counter weighting, but it is safer, makes the tractor handle better, and keeps the front axle loaded within its working limits so I would suggest it. (And so as not to be accused of being a hypocrite, I do use my loader without counter weighting from time to time for light work, so shame on me.)
Stay safe everyone!