So much of a Writer's work time is isolated. Social media is a huge tool new writers can use to get their name and work out there. It can help you attract and inform fans, connect with other writers, and is an attractive little bonus to have on your resume when shopping for agents/publishers. ;-) No really, my publisher totally asked about the extend of my social media presence, and they even offer author's extra books for being more present on line.
I hope this helps beginning writers get started in establishing your own online presence.
Just a post script of caution here, though; you can over-do social media, so use these tools at your own discretion. And, always, always, ALWAYS use it wisely. Protect yourself/privacy.