What are your limits? What are you okay with being out there? The companies that run these organizations are tracking you, and you should decide how much you're willing to give them.
Who are you willing to have see your profile? Different social networks serve different purposes, so decide beforehand what you want to make available to your coworkers, collaborators and students and what you want to keep separate.
Know what you have the right to do with your own work if you’re thinking of posting the full-text of anything to one of the networks. Check back in with your copyright agreements if it’s been a while since you signed them, or visit SHERPA/RoMEO (linked below) to see your publisher's copyright policy.
ORCID is a standalone open registry, and you'll also find that you're assigned identifiers if your works are indexed in Scopus (Scopus Author ID) and Web of Science (ResearcherID).
Citation indexes like Scopus and Web of Science track citations between articles, but do not always capture online discussion usage like social media and sharing. These tools, both projects of the nonprofit OurResearch, can help.
The Scopus algorithm uses the article metadata for publications in a journal indexed by Scopus to create Scopus Author Profiles when two or more articles are linked to one author name. Authors with similar names are assigned different Scopus Author Identifiers, but it is the responsibility of the individual author to ensure that citations are accurately assigned to the right identifier.
When you have a publication in a journal indexed by Web of Science, the algorithm assigns you an author record and Web of Science ResearcherID, which you must claim in order to eliminate duplicate records and inaccurate information.