I don't know why you have to use anything at all 90% of the time. A lot of times there's a business relationship between the equipment manufacturer and the product manufacturer. And some detergents leave more residues and put more junk into the environment than they should. I think the washing machine people would be hard pressed to tell you why you really need a specific chemical in your equipment!
If you have no smells, you don't need to do anything. Maybe every 6 months, depending on the type of water you have (hard with mineral deposits?) you might need to get rid of residues or build-up. I'd use 2 cups of vinegar in a full rinse and be done with it. I'd use 1 cup in a front loader that uses less water. Another option is baking soda - it's mildly abrasive and it rinses clean, and is a great odor-buster.
Chlorine bleach is pretty terrible for the environment so I won't use it anymore (dioxin is well proven to be a huge contaminant). There's no need to disinfect 99% of things in this world! I clean floors, bathrooms, toilets, the refrigerator and everything else with either baking soda (if something needs scrubbing) or vinegar (if a rinse will do it).