Smartaction will be able to capture notes when acted upon via email (i.e. Approve This is a good idea; Reject Not a good idea). Any notes after the action (i.e. Approve/Reject) can be captured by the workflow. This function is similar to Nintex' Approver Comments.
This is in comparison with Nintex On-Premise Flexi Task/Lazy Approval where you can add and process the comment.