Hi Danny,
The severity field has a purpose.
When you create a workflow inside Campaigns, it becomes a Campaign workflow. Execution of it is then handled by a parent workflow called Campaign Jobs or operationMgt.
This workflow identified how many concurrent processes it can run based on an option nms_LimitOCncurrency which is by default set to 10.
So, if you have to say 25 processes to be executed, if you wish to have your workflow make the cut, you can set a higher severity so that it can be accommodated in the available pool of 10 concurrent processes.
Regards,
Vipul