Back when I duck hunted just about every weekend of the season, I'd give the 870 a solid cleaning before the season, do some maintenance cleaning after each hunt, then give it a solid cleaning after the season was over and it was basically going to be in storage until next year.
Like Chemist though, I clean a firearm every time I shoot it. I know a lot of folks don't, but my grandfather instilled the marine discipline in me on that end.
For an 870, take the barrel off, take the trigger assembly out of the reciever, pull the bolt and clean and lightly oil everything. I'm a fan of Hoppes myself, but other powder solvents work just fine too.
A light shot of Remoil or 3-In-One Oil on the firing pin, trigger group and the slides from the forearm, reassemble and you are good to go.
I understand that an 870 is a workhorse and doesn't require the level of care than an AR or your favorite bolt action does, but the idea of never cleaning it or just giving it a cursory clean without the benefit of breaking it down and giving it a thorough clean and oil is just foreign to me. And hell, it's an 870. You can strip it down to it's basic components, clean it, oil it and reassemble it in about 20 minutes tops. Maybe I'm crazy, but 20 minutes here and there is a good investment in ensuring that your firearm functions perfectly every time for many years to come.