Mike Young writes:

Hence the question. "Hobby" range PMDC motors cost about twice as
much as "hobby" steppers of roughly equal speed and torque. Simpler
drives can be used with steppers, and the encoder is optional. So what
are the superior characteristics? The only that comes to mind is
static current draw for steppers; they draw power just sitting still.
That seems to be of very little consequence.

This kind of cost comparison isn't appropriate. Steppers perform
dismally. They are only "cheap" when they aren't moving, but the
purpose of the system is to move. Steppers are rated with holding
torque, but nothing like that torque is available in motion. The
"simpler" drive only works up to a few hundred rpms. To get higher
speeds you need a sophisticated drive that costs as much or more than a
servo drive. And the torque still dribbles off.

Torque is misleading you. Motion components should be compared in terms
of power, that is, torque times speed. Steppers start losing their
torque at rather low speeds, and that makes them much more expensive for
the equivalent performance of servos. The top speed is a fraction of a
servo.

Steppers are also absurdly inefficient in converting electrical power to
mechanical work. This means you need a power supply many times larger
than what a servo would require, and this adds further up-front expense.

Servos have guts. You can run them at multiples of their rated torque
for short periods. This is exactly what you need to move a mechanism
with stiction, which is to say any type of machine tool. Or to avoid
stalling on a cut with a difficult momentary load. With steppers,
moving and cutting is always stuck underneath the reciprocal of the peak
force requirements, instead of the average.

Steppers are appropriate for slow, tiny, low-torque applications, like
printer mechanisms and disk drive heads. They have no place in machine
tools any more, other than as a hobbyist toy to get the cheapest
possible motion no matter how dismal the speed.