What is the difference between dismissing and deleting a workflow?
Dismissing a workflow removes the instance of that workflow for that user. Dismissed workflows can be reinstated, if required, as they are retained in the system.
Deleting a workflow will permanently remove that workflow record from your portal. It cannot be reinstated.
Note: Only portal administrators can permanently delete workflows.
In some circumstances, a portal administrator may need to permanently delete pending workflows for a user.
For example, if a user has left the employ of the site and was removed from the portal, but their collaboration links to certain folders were retained. In this case, the deleted user would still have workflows triggered for them on any folder/document with a workflow assigned, that was collaborated to that user. The user will never complete them and they will remain as pending in perpetuity. As such, the user should be removed as a collaborator on these folders and the workflows should be deleted, rather than dismissed.
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Attached is a help document explaining how a portal administrator can permanently delete a Collaboration workflow.