What is a minimal step angle deflection for flight control surfaces? If the flight control surfaces (ailerons, elevators, rudder) are controlled digitally by servo motors, yet disregarding the way how the input to the servo motors get generated (manually or autopilot), what is the suggested minimal single step deflection of the control surface to be of practical value for a large UAV or piloted airplane? 

By "practical" I mean not a ridiculously small angle that slows down the servo with unnecessary many steps, yet sensitive enough to allow for a smallest practically useful deflection or ensure the precision of a small input. 

If the minimal step of deflection is not the same between them, then please suggest your answer for each control. Please give answer in degrees within 360 circle.
There are several phenomena that may affect the asked resolution. The easier one is the static (steady case), and the dynamic case which requires several more analyses. 

Statically, the resolution of any surface will determine the moments that that particular surface can generate. Consider the elevator, the resolution will determine which aoa and which speeds the aircraft will be able to fly (with a given weight and a given thrust configuration). 

Dynamically, the stability of the plane will derive the required resolution. Consider the elevator, and suppose your resolution is 1 degrees. The inputs will generate short period and long period (phugoid) modes simultaneously and your controller will become a bang-bang controller, because you can only command increments (decrements) of 1.

Hope these give some clues to understand the physics. For more details, control theory will be useful.