In today's world of social media, the meaning of the "like" button is beginning to expand. While engendered to express a genuine like, it has moved towards approval of a comment or status. Now, in terms of community management and user engagement, it is slowly becoming acknowledgement.
This acknowledgement is extremely important in letting users and fans know that they are being listened to. This acknowledgement is the difference between a one-time commenter, an active fan, and a social brand ambassador.
Unfortunately, whether it's your client's page, your fan page or just something personal, user engagement can be extremely tedious. Often, when you're posting content and generating multiple comments (whether 2 or 200), the question of when, why and who specifically you should engage with comes into play. If resources are short and time is limited it may not be realistic to comment back to every single person. So whom do you respond to without seeming as if you're a social robot blindly liking everyone, and why should you consider this?
WHY:
Strategically, liking a fan's comment can be used to foster a brand ambassador through the lens of positive reinforcement. The more often a one-time fan feels rewarded for engagement on a page the more likely he or she is going to keep returning and keep engaging. Essentially, the more foreign a user seems the more important it is to initially engage. And the more you consistently engage, the more you are strengthening their likelihood (pun intended) to return your page again. Think of it this way: you are building training wheels for that user to begin responding and spreading your message autonomously. But until they feel sufficiently rewarded through a response, they may feel like they're "unheard" and learn to ride somewhere else. You want them to ride your bike, not someone else's.
WHO:
Right now the intention is to foster loyal social brand ambassadors. But nevertheless, customer service is integral in social media and those with specific issues and complaints should always be responded to. Trolls however, people posting tangential/negative comments, do not need to be acknowledged. In fact, responding to a troll is only going to increase the probability that they will continually come back and saturate your page. When you respond to them you are rewarding them. Anyone posting something positive about your brand should be liked and rewarded. A thank you or conversational response will also due. Anyone asking a question should be responded to. Neutral comments should be acknowledged, whether liked or spurring more engaging comments. The goal of fostering a social brand ambassador is to convert neutrality to positivity and positivity to loyalty.
WHEN:
Now! No exceptions. The sooner you respond the better. Now stop reading this and start acknowledging your fans!