Seriously Asking!

Let me start this post by saying that I am SERIOUSLY asking this question! I am not trying to be sarcastic, annoying, witty, obnoxious...you get it! I would like honest and non-obnoxious responses to this question...ok, I may be willing to accept one or two funny (non vulgar) responses! Why do couples join their names on a facebook account? Is it out of convenience? Is it to be cute? Is it to be "one" or something? The reason I ask this is because I, like many people, often hesitate to contact friends who have this- why? Because I have no idea who is writing me back when they respond, and I also don't know who is reading it! Sometimes I don't have personal e mail addresses, so I use the little facebook message for convenience. I suppose I could send a message to ask for the personal e mail address, but in my defense people often give out joint e mail addresses, so it's possible I could have the same problem. I understand that spouses may have access to the other person's e mail or facebook, and many spouses share information with each other anyway, but still, as the sender of a message I like to know that it is going only to the person intended. I don't know how frequently spouses "snoop" or whatever, but I certainly and honestly can say that I do NOT just get onto my husband's accounts and read his personal mail. If it turns out it is common practice for spouses to do this, I am never sending a personal e mail message to a friend again! So if you have reasons you think people do this, or you are a person who does this yourself, could you please enlighten me as to the reason behind it? I really am just curious!