I know plenty of people here in the U.S. who have a middle name, including myself. I never really use it, but sometimes people prefer to go only by their middle name. But yet again, I know people who don't have middle names. I guess in some families, a middle name is to honour someone else in the family, eg.
Mary is giving birth to a girl, where she loves her grandmother and wants to honour her grandma's name, per se it's
Florence.
Mary decides she will name her daughter
Anna with the middle name of
Florence to honour her. So I guess it just depends :)