Why do some people have combined first names?

http://en.wikipedia.org/wiki/Double-barrelled_name

\"...Double-barrelled names may also be used by children who are not brought up by their birth-parents to combine the surname of a birth-parent with that of an adoptive parent, or the surname of their biological father with that of a stepfather. Other families believe that the act of consistently passing on only the father's name is patriarchal in nature, and choose double-barrelled names for feminist reasons, and for same-sex couples, to emphasise equality between partners...\"



This is what I found from Wikipedia, but it doesn't explain why some people have hyphenated \"first\" names (i.e. Mary-Kate Olsen).

Why do some parents name their babies in this way?


Also, it seems that many of my friends from Quebec have this particular type of names. Why is that?