We would advise against using a for-profit repository such as ResearchGate or its equivalents. These sites are useful if you are already a registered user, and using them can increase your work's visibility through Google. However, these social network repositories have some significant drawbacks when you compare them to institutional or subject repositories.
They may be prohibited by your copyright transfer agreement.
Some journals specify that you can only self-archive in nonprofit institutional or subject repositories. This means that if you upload your work, it may join the 7,000,000+ articles that have been subjects of takedown notices sent to these sites.
If we receive a takedown notice because your work has been shared in Digital Commons in a way that violates your copyright transfer agreement, we will reach out to you to identify if there is a version that you can make accessible that is in line with your publisher’s agreement.
They’re not as stable as institutional repositories.
Because of the for-profit nature of these social media repositories, their continued existence is dependent on their ability to generate a profit. This means that the site presence may be less stable than non-profit repositories, whose continued existence doesn’t depend on how much money they can make.
They’re making money off your work and gatekeeping accessing it.
For many of these sites, you need to register and create an account before you can upload a paper or even read or download someone else’s work. Like other popular social media sites, you are the product, not the consumer, and using these sites provides them with the resources to generate data that the company can keep and monetize. While they can enhance the visibility of your work, they are not fully committed to the Open Access principles which dictate most non-profit repositories and journals.
For more information, check out this blog post from the University of California.