A normal rule set can have an unlimited number of instances running at one time. For example, if a thousand jobs are marked as complete at the same time and there is a rule set enabled in the environment of those jobs (or the System environment) which triggers off Job Completed, 1000 instances of the rule set will begin executing at the same time. This is by design and is usually not a problem. However, there may be cases where having all instances running at the same time can cause problems, either because it will create too great a processing load on the system or the rule set is trying to use some resource that has limited capacity. In these cases it is desirable to be able to limit or throttle the number of instances of the rule set that run at once. By placing a Limit Concurrency action in a rule chain, the number of instances that run concurrently can be controlled.