On import I assign every image a "To Be Worked Label" using an import metadata preset. This shows up in my Workflow Label set assigned to red. These I flag as "Pick", "Reject" or leave unlabeled.
Besides "To Be Worked" (red), I have other labels that designate the stage an image is in my workflow.
"Work In Progress" (yellow)
"Needs Further Review" (green)
"Complete - Unpublished" (blue)
"In a Published Collection" (purple).
As I work pick flagged images, I assign a label that reflects the workflow status of the image.
Any image in the workflow label set that is red, yellow, or green can get marked for rejection. I am free to remove and delete any rejected image when the mood strikes.
I work Picked (P) images all the way through to getting assigned either a "Complete - Unpublished" (blue) or "In a Published Collection" (purple) label.
When I have worked the picked (P) images through to a Complete state (blue or purple), I return to the unflagged "To Be Worked" images for further critical review.