Energy consumption is a major issue for inertial drives with piezoelectric actuators that are integrated in autonomous devices. This paper discusses some theoretical aspects and some experimental results about the energy consumption of inertial drives with piezoelectric actuators. For a given velocity the energy consumption per traveled distance should be minimized. The step efficiency of inertial drives is deduced and should be optimized. Next, the trade-off between driving voltage and driving frequency is discussed. Some scale effects of piezo actuators for inertial drives are shortly discussed. Mechanical amplification increases step sizes, but at the same time lowers the actuator stiffness and so it lowers the limit of the driving frequency. The developed theory is illustrated with experimental results of four prototypes of a micro robotic platform based on stick-slip motion.