In order to avoid creating a negative performance impact on your system, you should understand how the different metrics in the job monitor uses Collection Services.
The data for the job numeric and summary numeric values metrics come from Collection Services. The overhead for obtaining this data is minimal and is not affected by the number of specific jobs that are being monitored. It takes two intervals of Collection services data before the first point or data metric value can be calculated. For example, if the collection interval is 5 minutes it will take more than 5 minutes before the first metric value is known.
The overhead for the job log message and job status metrics is much more costly in terms of the CPU resources required to obtain the information. Additionally, the number of jobs that are being monitored as well as the collection interval, affect the amount of CPU overhead that is required. For example, a job Monitor with a 5 minute interval will have six times the amount of overhead process to complete versus if the collection interval was set to 30 minutes.