Unsure Writers Forum why a pen name?

For those of you who have a pen name... What were your reasons for choosing a pen name? And did it fulfill its purpose? For quite some time I have seen many pen names. Such as Nora Roberts wrote for a while as JD Robbs (or some such). I mean heck. for all I know, Nora Roberts could be a pen name too. lol If you chose it for a writing reason (I am more interested in those who chose to do so for other than publishing reasons) what was the reason? For instance creative purposes. Did you choose to do so because once you did get published, maybe you didn't want your family to know that you had written about such a topic? Or did it allow you to say things under a disguise because you didn't want people to know that you wrote about them in a round-a-bout way? Please feel free to respond. I'm not here to pass judgement on anyone, I truly am interested on other peoples' reasons why. Thank you for reading. :-) .

I chose to write under a pen name because I didn't want friends or family to know that I have been using real life situations or encounters with them for my stories.  If people knew I would be in a heck of a lot of trouble.  Also I thought using a pen name would be truly awesome.