Wiping racks and oven after something splatters or spills will reduce how often you need to scrub the oven and/or racks. Some people use the auto oven cleaning cycle to clean oven & racks. However, this will dull finish on racks.

Annually. My oven's self clean instructions state not to leave racks in. So annually when I run the self clean clean cycle I remove the racks and scrub them.

Uh, I don't think I've ever cleaned the racks {blush}.

Every time something spills over onto the oven racks, they are cleaned. If spills are occuring so frequently, why not place a cookie sheet immediately beneath the bakeware? I prefer to clean spills as they occur, rather than expending extra time and elbow grease to remove caked on food from the racks.

I clean, it after I use it and while it’s still warm as so much easier to clean. I fill the sink with soapy water and wash with a sponge.