It seems to me like the main purpose of moderation is to make sure posts conform to the theme of the subreddit... to keep things on topic. Almost everything else can be taken care of by the downvotes of the community members.

A subreddit is like a community where every citizen has a gun. They can police themselves by downvoting each other... the only thing mods need to do is make sure the theme of the community stays on track.

I'm the sole mod of a subreddit with over 600k subscribers and I basically do nothing. My case is admittedly special because the subreddit is a weird kind of "game" with very specific, well-defined rules about how to reply to posts (and a bot that deletes replies that violate this rule), but in general I feel like people don't have enough faith in the ability of a community to handle itself. Occasionally I've had to ban people who are spamming /new with disturbing content, and I did end up setting some useful automoderator rules, but otherwise I find that the community runs itself.

I've gotten a few messages from people over the years saying they're unsubscribing because they wanted me to take a more involved role in moderating the content posted to the subreddit, removing posts they thought were "low quality". That's fair, but I don't think it should be up to me what counts as "low quality"... I'm just one person. The beauty of a community is watching it develop organically from the actions of thousands of people, not molding it into some shape you happen to prefer. It's like an organism, and it has a mechanism to achieve homeostasis: upvotes and downvotes.