@stoneMason-- You can but you don't have to. Although allegory and metaphors may often be seen together in a piece of work, they are definitely not the same.
Allegory is symbolism and in my opinion, it is usually hidden or not very apparent immediately. So for example, let's say there is a poem about a sick man and how he needs to be treated. One may read this poem and believe that it is just about a sick man. But the author may reveal that it is actually an allegory about a country at war. The sick man may be symbolic of a war torn country and peace may be the remedy required. But you might never know this without a hint of some kind.
A metaphor, on the other hand, explains something by likening it to something else and it is always very apparent. There is no confusion about the metaphor "life is like a box of chocolates." It's very obvious that life is being likened to a box of chocolates.
I think it takes more skill for a writer to use allergory and it also requires a careful reader to know it when he sees it.