My concern would be tool pressure deflection. If you achieve repeatable
results with various materials, then I'd agree, level, at least for your
machine, may not be important. However, it may reflect the fact that the
spindle is not parallel to the ways. If that's the case, twisting the bed
can resolve the issue, assuming it's twisted in the proper direction.
Problem is, it's difficult to make the determination----which is why
leveling is recommended. That makes the reference plane easy to remember.


Yep, its important to remember the lathe and part is made of cheese.
it deflects under load. This effect is far larger than any alignment
issues. acutually easier to handle on the cnc, just command a taper
cut.

Now trying to hold a couple tenths on a long part in a manual lathe is
a real challenge. Thats why they pay real machinists the big bucks.

Karl