Though I have been critical of https://www.academia.edu/ I can also see good, and I greatly appreciate the feature where people can comment on why they want to download an author’s paper.

When an author is writing for different audiences or for a new one, comments explaining where and why a publication has been helpful is encouraging and useful feedback. For new academics, these comments can be used for promotion and so on, but even us older academics can appreciate a few words of feedback and even constructive criticism!