Reservation, a tool to reduce the balking effect and the probability of delay. We investigate a threshold reservation policy implemented within a single customer’s class. From an explicit performance analysis, we prove that the potential of reservation is into the reduction of the balking effect together with a higher server’s utilization. However, it also may result in a higher expected waiting time and more abandonment. We conclude that reservation can be efficiently implemented in large systems, under high workload situations, with a low waiting aversion and a low impatience.