Suppose there is a failure in the workflow involves where human intervention is needed. (Add balance to the account (OR) some data to be added on manual recon).
We know that the flow will work after that. Now, how can we retry the flow after the above changes if it is critical and we can not wait for the next scheduled retry.
PS: In the above case, there is no code change due to any bugs but there is state change by external events.
You can implement this as part of the workflow code (or even as a workflow interceptor to make this generic). The workflow would listen to a signal. When this signal is received, the workflow state is updated, and the activity is canceled and rescheduled immediately.