This controls the number of concurrent builds that Jenkins can perform. So this value affects the overall system load Jenkins may incur. A good value to start with would be the number of processors on your system. Increasing this value beyond that would cause each build to take longer, but it could increase the overall throughput by allowing the CPU to build one project while another build is waiting for the I/O. Agents may not have zero executors. The default value is assumed if an invalid value is entered.