Million instructions per second only related to the central processing unit speed. A big negative about million instructions per second is that it does not take into consideration the fact that different instructions could take different times.

Instructions might take time based on different factors like input output/speed, memory, storage capacity, processor architecture, or programming language used. This often results in a computer performing faster with a lower million instructions per second rating than with a computer which has a higher value for same. Again, this benchmark is incapable of providing the information of how the processor works and whether it is suited for a particular application or not.

Million instructions per second is however useful in comparing the performance of processors based on similar architecture. It can give a clear picture of task performance speed rather than just instruction execution speed.

Again, there is no standardized method available for providing the measurement. As a result of the given reasons, million instructions per second measures are not used much.