This controls the number of concurrent builds that Jenkins can perform. So the 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, because it allows CPU to build one project while another build is waiting for I/O. Slaves may not have zero executors. Assumes default value if invalid value is entered.