When a torsion axle wears it develops negative camber and some tow out.
These conditions result in excessive wear to the inside edge of the tires
I just switched out my axle after 16 years and well over 80000 miles.
I seldom bothered to lift it for storage even though doing so is a good thing.
That axle was in good shape , but I wanted 10" brakes
and a zero angle.
When new... a torsion axle will take a set within the first < 1000 miles, dropping the height 1/2"-3/4" with a near rating load.
Subsequent drop is gradual and associated with normal wear as mentioned above.
Of course damage, constant overloading, or manufacturing defects can be exceptions.