On the surface, interest-only mortgages sound like a bad idea when buying a home in Philadelphia. It's a type of mortgage instrument that has the payments going towards the interest on the mortgage without touching the principal. You're probably thinking that means you'll pay only the interest on the home and won't even own the front door for years. While this is true to an extent, that's not all there is to an interest-only mortgage. The up-front interest payments only last a certain amount of time and are no riskier than a traditional mortgage. In fact, they offer more financial flexibility than a traditional mortgage and here's why.