The University of California Office of Scholarly Communication has a really great blog post about the difference between open access institutional and subject repositories and academic social networking sites like Academia.edu and ResearchGate.
Here’s the post: http://osc.universityofcalifornia.edu/2015/12/a-social-networking-site-is-not-an-open-access-repository/
I particularly like the table they created to demonstrate the differences:
