If you are a parent and have failed to purchase the washable crayons, you have probably had to deal with crayon stains – either before they went through the wash, or after the entire crayon itself went through the washing machine.
To remove those pesky crayon stains, spray the crayon stain with a prewash laundry spray, then flush the spot with hot water. Then wash as normal.
If your kids make regular messes with crayons on clothing (or bedding, or walls!), it is probably cheaper to have the added expense of washable crayons than cleaning up after the mess made with non-washables.