Some magazines, including My Weekly and People's Friend don't like the same author name appearing twice in the same magazine. If more than one of your stories are selected for the same issue you'll be asked to provide a pen name. This happened to me recently and I selected two names I'd used for characters as I'd already checked these weren't the real names of anyone famous.
You might be asked to provide a pen name if your real one is the same as another author's or you usually write in a very different genre to that which the magazine publish. Or perhaps you'll have your own reasons for using one.
Have you ever needed a pen name? How did you choose it, or how will you pick one if you do get asked?