What is the purpose of a buffer in the theory of constraints (TOC)?

A buffer in the theory of constraints (TOC) is a level of inventory that is placed before the governing constraint or the bottleneck to prevent it from being starved or idle. Buffers are used to immunize the system’s performance from variability in demand or production. Buffers are part of the drum buffer rope method of scheduling and managing operations that have constraints. The purpose of a buffer in TOC is to prevent unplanned idleness of the resource, which is the most important factor that determines the throughput of the system. Throughput is the rate at which the system generates money through sales. If the resource is idle, then the system loses potential throughput and profit. Therefore, buffers are designed to ensure that there is always enough work available for theresource to process, regardless of any fluctuations or disruptions in the upstream or downstream processes.

References: Theory of constraints - Wikipedia; Drum Buffer Rope and Theory of Constraints - opexlearning.com.