The amount of garbage is pretty highly dependent on the board - the entire site isn't /pol/. If you're willing to be your own content filter and can handle a lower signal to noise ratio than a curated community there are a lot of good posts. It's DEFINITELY not for everyone though.
For example, 4chan has some of the most up-to-date English language discussions around for a lot of Japanese fandoms. If you want to discuss new releases of obscure japanese noise bands, you probably want to be /mu/. If you're not on /mu/ and are on some other platform, you're probably just going to get a regurgitated version of the discussion from /mu/ anyway, with an increased propogation delay and someone else doing the cherrypicking. (Note: I'm just using "Japanese noise bands" as an example, I don't know if that particular discussion on /mu/ is good, or if the relevant low-latency discussion is on Twitter, Tumblr, Reddit, etc these days)
For example, 4chan has some of the most up-to-date English language discussions around for a lot of Japanese fandoms. If you want to discuss new releases of obscure japanese noise bands, you probably want to be /mu/. If you're not on /mu/ and are on some other platform, you're probably just going to get a regurgitated version of the discussion from /mu/ anyway, with an increased propogation delay and someone else doing the cherrypicking. (Note: I'm just using "Japanese noise bands" as an example, I don't know if that particular discussion on /mu/ is good, or if the relevant low-latency discussion is on Twitter, Tumblr, Reddit, etc these days)