The use of step function reference commands is often discouraged when the system has flexible dynamics. The rule of thumb is that smooth commands, such as S-curves should be used instead. This paper attempts to dispel the myth that step functions are inappropriate for flexible systems. To accomplish this, a new approach for analyzing the response of systems driven by smooth reference commands is presented. This approach treats S-curve command profiles as input-shaped functions. Input shaping is a method of reducing residual vibration by convolving a sequence of impulses with a baseline system command. The sequence of impulses is the key to predicting the system’s vibratory response. By interpreting S-curve commands as input-shaped functions, common criteria for comparing the two types of commands can be developed. The results indicate that sequences of step functions are much more effective at reducing vibration than S-curves.