Unless you've never been cheated on before your probably on edge about your boyfriend or girlfriend being able to follow and like anything. And it aids IN cheating so unless you completely trust your partner not to want to hit on other women or men then yes it's bad :P
I met my husband on social media ( on a gaming forum ) and that's the best thing that had ever happened to me I believe. We communicated through social media for 3 or 4 years until we finally met in person. We Skype and texted. However, we never were involved in Facebook or any sites like that. We trusted each other that each of us wouldn't cheat and we never did. We never had the interest of any other people, we only wanted each other. But from other people's relationships, I have seen social media destroy relationships. (From my opinions, those relationships weren't going to last anyways). I have seen situations of the man chatting to other girls on Facebook saying they are cute or funny and complimenting them. I have seen women do the same to men. In my opinion, you could call calling some one other than your partner "cute". Social media can also create suspicion and jealousy which can also doom a relationship. Social media can either help a relationship, like mine, or destroy a relationship, through unloyal and unfaithful partners.