One of the more popular book sharing sites I'm aware of used to be a place that people could easily upload and more importantly, download a PDF of either legal but usually copyrighted, i.e. illegal, material. Over the last couple of years the site apparently decided it was time for them to make money, so they did what countless other sites did, started charging a subscription.
While this sounds like it shouldn't make much of a difference, the problem is that those people looking for free stuff aren't going to change. Even if it's only $8.99/mo, that still goes against their DNA and they're not about to become someone they aren't.
On the other, this is welcome news to the publishers and other copyright holders. If a free PDF download isn't easily available, then it's more likely that a legal sale will happen. Much as I'd like to think that your average Joe wouldn't knowingly download illegal material, that's simply not the case. Most do.
When it comes to piracy, removing the "low-hanging fruit" is about as good as a publisher can hope for and when a free site decides to make a profit and go subscription, that's good too.