In a pipeline you can choose to have a workflow on a pipeline task. The strength of workflows is particularly apparent when combined with pipelines, providing a birds-eye view of the status of a pipeline.
In the following example, an art Sign off workflow has been select on pipeline tasks "Low LOD" and "High LOD". The Low LOD step, when completed, will be assigned to the art lead for review.
The art lead now has the task in their To do list, ready for review.
The art lead can choose to either approve or disapprove of the quality of the task. As per how the workflow was designed, Quality not approved will send the task back to the artist for further work.
In the Planning section the pipeline indication will now revert to "Low LOD" and "High LOD" because the quality was not approved (and the item was set to Not done). This will re-assign the task to the artist.
The artist again has the task in their To do list.
This review loop can continue indefinitely until the art lead sets the task to "Quality approved."