It adds some amount of "proxy content". But right-click or long-click and block the channel on the stuff you really don't want. Also if you watch a video you thought was interesting but it was lame, go to history and remove it.

And finally if you regularly watch stuff subscribe, it's a strong preference indicator.

I do get some junk in my feed now and then, but mostly I discover good stuff I enjoy. And that includes really small channels.