I recently noticed this when answering one of my own questions.
After I've added my answer, the 'Add Answer' button is replaced with 'Add Another Answer'. Why do we have this feature? Surely there can only be one answer to a question (per person). If they have more to add, they would simply append to, or edit their original answer?
I have seen instances on SO (or it may have been programmers.SE) where there have been 'two sides' to a question - i.e. a debate - where the same person answered for both sides of the argument and received a number of up votes on each answer. Maybe it made sense to allow that user to post two separate answers since they were from completely opposing viewpoints, but then if that is the case, the question in question (lol) isn't a good fit for the Q&A format and would be more suited to a forum discussion platform.
Why allow multiple answers from single users?
I just saw this question on the same topic whilst writing this, but I don't think I've ever stumbled across a question where a single user has posted multiple answers/solutions and not just put them all in one answer.