Electric motor and no load speed

[bonzer]

Hello everyone! Please help me to figure out the concept of no load speed.
I find that from mathematical point of view we have no torque when there's no load so the motor needs no current to work. For example a SPM motor , without a current we still have a speed due to the voltage applied and the permanent magnet flux linkage and considering no resistance it's equal to back emf.

V= Λ_mω

I'm new into this but what I think is that the motor needs always a current to work because of its physical structure it is a mechanical load itself. Maybe it's negligible compared to the currents it can work at with big loads.
So I don't understand what is this information used for? Is this an approximation?