Google's John Mueller made any confusion about what to do with low quality content made clear when he was asked about it in a Hangout.
First, Mueller gives a non-technical definition of low quality content:
"So in general, when it comes to low quality content, it's something in which we see your site is providing something, but it's not really that fantastic."
What should you do if you find low quality content on your site?
There are two approaches, says Mueller, so do not jump to the conclusion that content should be deleted.
The best solution is to keep the content where it is and improve
"There are two approaches to addressing this. On the one hand, you can improve your content and, from my point of view, if you can improve your content, probably the best approach possible. "
Really take a look at the content and think why you posted it first. If it has a purpose, make sure you've been able to assign more value to the article.
"You clearly had a reason to put this in, now be serious about the content you've put in and make sure it's useful"
Maybe deleting content is a better option
Mueller adds that there may be circumstances where content exclusion is the best option.
Sometimes you may not be able to improve low quality content because there is so much or maybe it has been generated automatically.
Rather than improving some content and not improving others, Mueller recommends being consistent and cleaning everything.
So you have it. If there is poor quality content on your site that can be improved - do it. If you can not, get rid of it.