Every hiring manager has a story about someone who has botched a job interview or torpedoed a career due to thoughtless comments on social media sites. I know someone whose close friend, a technical writer, lost his job after making negative comments about his company’s investment prospects on MySpace (remember them?).

Few people think twice about posting embarrassing party pictures on their Facebook pages or casual trash-talk on Twitter. However, your prospective employer or current company also has an online presence, so you are the face of the company. Accordingly, they may keep an eye on you, which is not tough when you voluntarily post content for the world to see. As your mother always taught you: don’t bite the hand that feeds you. Moreover, if you can’t say something nice, don’t say anything at all.

As painful as harpooning yourself can be, time waste represents the true danger here. Yes, I use social media, and you may use social media at work for valid reasons: you are in marketing; you are in HR trying to recruit people to your company; you are an entrepreneur reaching out to prospects to gain more business; you are networking for a new job; or you are staying in touch with customers.

However, many uses of social media aren’t work-related and represent wasted time. The traditional work-year clocks in at 2080 hours, or 260 work days annually. Suppose you spend 10 minutes each workday Tweeting or checking Facebook when you should be working. That comes to 2,600 minutes a year—over 43 work-hours, down the drain. If your manager decided to deduct that at the end of the year, you’d have over a week less PTO.

Unless social media provides part of your income or your job requires you to monitor it, then it has a lousy Return on Investment. Even if you do use it sensibly at work, it may still have a poor ROI. Do you know the time you spend on it yields correspondingly high results?

You’d kick anything else with a bad ROI to the curb, so if it isn’t providing proven results, tune out, drop out, and refocus on what matters. Save Facebook, Twitter, and the Pinterest for your non-work time. Even then, take care what you post—because everyone’s on the Internet nowadays.

Does social media provide a high ROI for you? How do you keep your social media usage in check?