Whether you're currently employed or hoping to be, here are some reasons to take the time to develop your online profile and expand public awareness of your research.
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). If the public is paying for your work, they should be able to understand what it's about.