I use it to download books I bought but can't be downloaded anymore because Barnes and Noble bought the publisher/online-retailer and forbid downloads from non-US citizens (yep, that is a thing).
DRM related too. I bought books on Kindle but recently trying to highlight and process my reading notes more. Turns out publishers can set an upper limit to highlights (e.g. 20% of the book) and just cut the highlights off randomly. Infuriating, and I end up re-downloading those books (and more) off of libgen so I know my highlights are reliable.