Actually, several stories shall be addressed:
*As a producer, I need to be able to stop running workflows, so that I don't need to wait until they finished *
Use case example: Too bad if a producer has started a workflow just to find out a little later the he needs to first adapt metadata or cut the video. Currently, the producer needs to wait until the workflow has finished processing (can take hours) before he can apply the changes and start the workflow.
If the producer could stop running workflows, he wouldn't have to wait for hours...
As a system administrator, I need to be able to delete workflows
Use case: In support cases where many workflows were started but all failed (until the last one that fixed whatever the problem was), it is desirable to not keep all the attempts to fix the problem (usually requires starting workfows) in the history.
On the other hand, it is undesirable that producers can delete workflows as they normally shouldn't.