I think personally it's somewhere around 50%. Whenever I've reported more posts than I've written I think it's time to take a break and do something else for the rest of the day.

The thing I'm finding most useful about the report history page is I don't have to spend time trying to find things in the modlog to know what happened. I've never really known whether what I consider to be a shitpost is worth reporting, but so far every one I have done has been deleted.