I have been promoting ResearchGate to my students. But, recently, I noticed the information in RG lags GS in terms of citations. So, recently I am thinking there are other benefits to RG that I am not aware of them.
They are different tools. Research Gate is more for promoting your work and to access other's work thorugh networks and contacts. Google Scholar is to register activity on published works on web, including citation.
To me Google Scholar, in its use, is closer to ORCID or Scopus Authors, than Research Gate. RG is closer to Academia or other services for networking or promoting works that could be cited further.
In addition to what Nicolás Arias Velandia wrote, RG has various possibilities for interactions between members - follow other members and projects, send messages, add comments to publications, ask questions, participate in discussions, etc. It is a social network for researchers. See also https://explore.researchgate.net/display/support/Getting+started.