If you have a very common or often misspelled name, use a nickname, or have work published under a maiden name, one useful tool is the ORCID, a unique identifier that you can use to collect your work under your exact name, and then use when publishing future works.
You are Googleable and people will do so, especially if you're in the market for a new job. Proactively creating profiles and perhaps establishing a blog will help ensure that your top results are the ones you want people to see.
Formal and informal studies have shown that work promoted through social media gets more views and downloads than work that isn't. There are a number of tools that will help you coordinate your promotional push. Similarly, find the work of other scholars through means you might not have come across otherwise.
Meet people across the country and the world who share your research interests. External collaboration increases your institution's profile and can look good to promotion and tenure committees.
This is especially true of federal agencies. Dr. Denise Barnes of the NSF puts it this way: “It is imperative that NSF staff and those funded by NSF be able to communicate in a clear, concise and compelling way the outcomes and impacts of taxpayers’ investments and do so in a manner that is easily understood by a diverse group of stakeholders who span broad technical literacy levels. Effective communication can help stakeholders grasp the societal benefits of NSF-supported research and education undertaken in the nation” (quoted in Shipman 2012). The public is paying for your work; they should be able to understand what it's about.
Shipman, M. (2012, December 5). "SciComm matters because... funding agencies say so" [blog post]. Retrieved from http://www.scilogs.com/communication_breakdown/scicomm-matters-funding/
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.