I use Facebook for a set number of things. Promoting my writing, keeping in touch with family, friends and professional colleagues; making sarcastic posts on other people's walls; and posting fake celebrity death news. On occasion I will do a more personal post, but I don't make a habit of it, and there is a reason why.
First, I'm private. I just don't need people knowing what I'm doing. It's weird, and I'm not vain enough to think that anyone would care. I'm not that self-important, which I tend to think Facebook really promotes. I also find posts where people tend to post such information to be odd at best. I don't know what to say to someone who posts, "I'm sitting at my table with sushi." What do you say to that? It's fine if people want to post that, but with few exceptions I will abstain.
Facebook has been a great tool for marketing my writing and for making friends and family uncomfortable. Beyond that, I could leave it behind and not worry about it one bit (and have often thought of that). People act much the same way on it as they do in real life, too, despite the general consensus that it is otherwise. They talk about petty things and take offense to the most innocent of comments. I have text messaging and e-mail for the latter, and I try to avoid the former at all costs.
So, dear friend, that is why I don't post more on Facebook. Nobody needs to have an up-to-the-minute update on my actions, and I have no desire to tell anyone, either. I stopped reporting in when I was about 14, and I was a much better person for it, too.