A single finite-capacity machine that can process several product types requires a set-up that is capable of allowing adjustments in machine settings to complete a particular job. The family-based scheduling rule (FSR) can be used to improve performance by reducing the set-ups resulting from hard-pressed capacity. However, the waiting time of jobs on queue increases and fluctuates, so the mean and variance of the flow time of jobs also increase. In this study, a decision criterion to evaluate the effects of capacity saving is developed through a change in the considered dispatching rule from the first in first out (FIFO) rule to FSR. This decision criterion can be used to determine in which condition the set-up time can be significantly saved through a replacement of FIFO with FSR and thus help in making a choice between FIFO and FSR.