Wheel weights are good for plowing, snow blowing, pushing or pulling, but weight on the back of the tractor is better for loader work. A load in the bucket will use the front axle as a fulcrum and take weight off the rear of the tractor. Weights and loaded tires will counter this, but not as good as weight out back. Weight out back will use the rear axle as a fulcrum and help ease the strain on the front axle.
If your plowing snow, weights and loaded tires are your best bet. There is no weight out front when plowing or snow blowing because the implement is on the ground. In this case weight out back can affect your steering and make it a bit light. Wheel weights and loaded tires plant there weight right over the rear axle not affecting steering.
Obviously, the bigger the tractor, the less you will notice.
Dave