None, of course. It's possible to disable ads for users with Web Monetization, but it's also possible to be greedy and use both at the same time. But remember, we're not talking about big companies or anything of the sort, it's more for small scale personal blogs, or, as i pointed out, institutions like the Internet Archive or Wikipedia, so greed is IMHO unlikely and will probably be rare.
In any case, if you use an ad blocker, which you absolutely should, the ads don't impact you.