Industrial psychology sets forth that human knowledge has an impact on performance. Literature on information systems proposes that usefulness of an information system also contributes to performance results. An economic approximation suggests that people and technology are substitutable factors to produce outputs. This study focuses on analysing the substitution effect between people (based on their knowledge) and technology (based on its usefulness) in different automation levels. We gathered data from 125 users. The results show that the higher the level of automation the lower the effect of knowledge on performance and higher the impact of usefulness on performance. The design of information systems can use this moderating effect to assign tasks (between individual and technology) based on convenience and timeliness, but the negative factors of a higher level of automation should be taken into consideration, such as impairment of the employee’s knowledge.