The processor only spits out step and direction signals. The motor driver chip/module interprets the step pulses as full steps or microsteps depending on jumpers or programmable settings (A4988, DRV8825, etc), or dip switches (external modules). Varying the step size on the fly will require the CPU to perform additional processing (as well as PCB modifications). If you're already concerned about the CPU being a bottle neck, adding additional processing like variable microstepping is only going to make it worse.
A 200 step/rev motor will provide highest resolution at 16 usteps/step and both are typically used in a 3D printer. Higher usteps/step will smooth the motion without providing any increase in resolution. Also, the higher you set the microstepping, the lower your maximum possible print speed due to CPU limitations (100k pulses per sec for smoothieboard). Print quality is inversely proportional to print speed due to intertia of moving components, among other things. There's not much point in using 16:1 ustepping to get high resolution if you're going to be driving the thing so fast that it makes sloppy prints anyway.
A 200 step/rev motor will provide highest resolution at 16 usteps/step and both are typically used in a 3D printer. Higher usteps/step will smooth the motion without providing any increase in resolution. Also, the higher you set the microstepping, the lower your maximum possible print speed due to CPU limitations (100k pulses per sec for smoothieboard). Print quality is inversely proportional to print speed due to intertia of moving components, among other things. There's not much point in using 16:1 ustepping to get high resolution if you're going to be driving the thing so fast that it makes sloppy prints anyway.