I keep pretty active on the three major social network platforms; Twitter, Facebook, and Google+. Yes, it’s a lot of work to keep up and post content for all three but I do it for a very particular reason.
The reason is audience. I have built an audience of people who are interested in what I have to say and likewise I am interested in them. The problem is that audience does not exist in one convient location. Some of them love Facebook and spend all their time on it. Others prefer Twitter while some are hooked on Google+. Sure a few cross networks but if I were not active on all three, I would absolutely miss some people.
If you are using social networking for personal reasons, you might just want to choose the network you like best feature-wise or where the greatest number of people you know are. However, for business reasons, you need to reach the largest audience possible. Since I do use social networking for both personal and business reasons, I have chosen to participate everywhere. I am actually also active on some niche social networks including Instagram (photos) and Pinterest.
How many networks you choose to participate in is largely a matter of your personal bandwidth and how strongly you want to serve any particular network. Obviously, the more you split your time, the less each network will get from you. Honestly I will tell you I don’t split my time evenly. I put more time into Twitter than any other network, Google+ is second with Facebook not too far behind. Some days/weeks this percentage my change, but this seems to be my overall ratio.