On SharePoint 2010 or MOSS 2007 with SP1, we cannot trigger workflow automatically as system account. But, if we want, we can manually force the workflow to run under system account. This is useful in Development environment.
But for SharePoint 2013, it's different.
We still can manually run "SharePoint 2010" edition workflow on SharePoint 2013, but, for "SharePoint 2013" edition workflow, once the workflow is triggered, the "Internal Status" of the workflow instance is first changed to "Started", then end as "Suspended".
So, we have to run workflow as "non-system account", even in Development environment.