Worker multifunctionality has been recognized as a tool for enhancing system flexibility and performance. This paper investigates the impacts of worker multifunctionality in a heterogeneous serial production system in the presence of individual differences in experiential learning and forgetting. The tradeoffs of multifunctionality and cross training are examined in conjunction with several process characteristics and operational decisions including staffing level, system bottleneck position, task similarity degree, and worker rotation interval. The results show the relationships between the preferred level of worker multifunctionality and both process characteristics and operational decisions. In several cases, minimum multifunctionality and short worker rotation intervals provide improved system performance. Additionally, process characteristics, such as the position of the system bottleneck and the degree of task similarity, have impacts on individual learning--forgetting behaviors and, subsequently, on decisions relating to multifunctionality levels and system performance.