Let me give you an example. Hubspot uses scribd like a religion. The biggest content marketers use those document sharing sites as lead funnels. And they work.
I know because I always find myself downloading pdf's, videos, power points, excel sheets. etc. Truth be told, a buyer tends to download resources more than reading a blog.
So yes, use them wisely and they can work wonders for you. For example...write a blog, repurpose it into a pdf, post it on your website as a free download when they join the newsletter, post it on your scribd channel. Don't allow full reading of the pdf until they come to your site. Repurpose it again to a short 3 minute video. It works.