Despite a general consensus that use of information technology (IT) is an important link between IT investments and performance, the extant literature provides only a limited explanation as to when the use of IT lifts performance. We posit that the impact of knowledge management systems (KMS) usage is contingent on users’ alternative sources of knowledge as well as their specific task environments. We investigate under what conditions repository KMS use leads to higher performance outcomes in a retail grocery context. We use a unique longitudinal dataset composed of objective measures of KMS use and sales performance of 273 managers over 146 weeks collected from a retail grocery chain. We obtain two main results. First, we find a diminishing impact of KMS use for managers who also use other sources of codified knowledge, namely physical or computerized alternative knowledge sources, whereas a complementary relationship seems to exist between KMS use and social sources of knowledge.