As with everything, size does matter and each tractor/setup is different.
When I got my little
B7300, it had loaded rears, but I noticed the rear end was still light at times with a loaded bucket. I chatted with my neighbor, a diesel mechanic who frequently works on farm equipment, and asked him to weld up a ballast box for me, which has helped immensely. Basically it will hold 10 solid blocks, for about a 320# combined ballast on the 3PH. Since then, I have noticed a need for a bit more weight, and solved that by ratchet strapping 4 more blocks to this setup. I may have him permanently weld on some added bracing to handle this. [Splitting wedges are low cost shims that keep blocks tight/steady during work]
I do have to admit, the loaded tires were an added benefit and are great. I have mowed with my cousins small JD with his MMM without loaded tires, and it feels much less stable when mowing inclines than with my
B7300. Also, I have my rears adjusted wide (per manual) for added stability, at all times.
And, as has often been warned, and often needs repeating, never travel with a loaded bucket raised to height. Always keep the load as low a possible. Save raising the bucket until stopped or nearly stopped at location to dump or empty.