Loaded tires give you rear ballast to counter act the weight of the loader on the front end. It will make the tractor more stable on a side slope because the weight is placed down low; it won't make the tractor feel "springy" when you go over a bump; it'll give you better traction; and since the weight is in the tires and not directly on the axle or rear end like wheel weights or a ballast box would be, it makes it a less stressful ballast alternative for the tractor. One thing though is you can't remove tire ballast in the simple way that you can a wheel weight or such. But to me the immense benefit that loaded tires gives you will counter act every other form of rear wheel ballast.
I have the rears on my 3320 filled with Rimguard, it cost me $175 from the dealer. Rimguard is basically beet juice, it's not corrosive, it's non-toxic and bio-degradable so if you puncture a tire it won't harm the environment, it has the highest lb per gallon ratio of any type of tire ballast, and it's freeze resistant down to -35. IMO, it's the ONLY choice when it comes to tire ballast.
