Comments add an extra layer of accountability and communication between all members involved in a workflow.
With comments you can:
Leave a comment detailing your progress
Enquire about the progress of a task
Reply to a comment from other members in the workflow
To add comments on someone's task(s) in workflows:
Go to Workflows on the side navigation menu and click the Workflows tab.
Select the particular workflow and click on the task you want to comment on, leave a comment, and click on Save.