We're supposed to do that?

Pretty much what Tishtosh said. I will add one thing....

3. when it is time to paint.

Sometimes I use this skinny flat-ish thing that was made to clean out the dryer vent, but it sort of fits under the washer and dryer and fridge. It's sort of like Oakley's red Oxo duster and it's washable of course.

When I move. No exceptions. :-)

I try to do it twice a year for kitchen appliances. The last time we pulled out the fridge, we found enough fur under it to make another cat.

What May said. My appliance guy said at least once a year. I couldn't believe the amount of cat hair stuck to the vent area in front of the refrigerator when we had the new one put in. I mean we're not dirty people and...just wow.

Only when I need to move the appliance for some other reason.

When I buy a new one

ok...so it's just not me. Assuming none of my appliances die within the next 6 months, I'll pull them out again in 6 months and see how much dirt accumulated.

Just be careful with the fridge. I have had three significant kitchen floods from service people "helping" me out by moving the fridge. Painters, housekeepers and appliance repair people. Thanks for all your help!

Don't do what my husband attempted in our old house. He put the leaf blower nozzle under it to blow out the dust bunnies...

Needless to say, I was sleeping in that morning when this horrendous whining motor started up and WOOLY MAMMOTHS started flooding down the hallway into my bedroom. The sheepish look on his face was priceless. His is my version of Tim the Toolman Taylor. IT took days to clean out the mess. (Now we have one of those flat vacuum nozzles designed for small spaces under appliances.)

Loonlake: something like this? Looks like a good idea.

https://www.amazon.com/McNaughton-40115-Exten-Vacuum-Attachment/dp/B00L5KMPCU

I don't understand how I have cat hair under there and I don't have a cat ! ? Not very often apparently but I can tell you that a major flood flowing rapidly through your home will clean it out ! Appliances might not work though .

Monthly when Ben was alive, but since he died a few months ago, the cat hair is limited so a quarterly vacuum works. I also have a modified furnace filter over the fan/compressor area. I change the filter every 6 months.