If your the type of person who likes to interact with people on the Internet and use an Android mobile phone, then you should at least have the three basic social apps available on the Android Market. These three mobile apps for Android addresses three different aspects of social networking. The frequency of using them deepends on what you do and who you are. You should at least download and install them to try out whether you really need all of them.
The three basic social networking apps for Android I am talking about are the Twitter app, Linkedin app and Facebook app. All three of them have official versions which you can install on your Android phone.