At the Project Configuration level there are a variety of governing settings that control how jobs are handled for a specific project.

In some systems it is desired to limit the number of scheduled jobs a user can run at one time. This setting is going to determine the number of scheduled jobs an specific user will be able to run at a given moment. If more jobs are scheduled to run, they will need to wait until previous jobs executions finish.
This can be confirmed by checking the DSSErrors.log file. A message similar to the following will be logged when this governing setting is violated:
[Kernel][Scheduler Trace][0x80043033] Number of jobs has exceeded maximum for project 2.[2][Strategy Tutorial]