Microstepping stepper motors
Microstepping has the effect of increasing stepper motor power consumption above what it can be under standard stepping conditions. 

A stepper motor when used in the conventional one-step per physical position mode latches electro-magnetically. Two conditions apply.  


i In the stable "home" position power may be removed and the motor will remain in that position unless perturbed with a torque in excess of the specified holding torque.  
ii The user may elect to continue to apply voltage to the coils with the same polarity that caused it to step to the current position. This may be full stepping voltage or some reduced voltage. This applied voltage will increase the holding torque but also add to the power consumption


In microstepping the motor is held at some intermediate position between two "steps" by applying PWM to the windings in some ratio that on average holds the motor in an intermediate state. (With some coil arrangements it may be possible to apply two different analog voltages on two windings to maintain an intermediate position but this is (probably) less likely).
However it is achieved, holding an intermediate micro-step position requires holding the rotor dynamically between two potentially zero energy electromagnetically stable states. 

So  


At best, microstepping uses no less power than an arrangement where a holding voltage is applied to the windings when the stepper motor is in a stable "home" position.
Compared to situations where a stepper motor sits in a stable home position with no more reduced voltage applied the microstepping mode uses more energy. How much more depends on the ratio of stationary to stepping time used in the normal mode.