In reading up on good practice for database applications I've frequently come across advocates of so-called "business logic layers" and I'm trying to decide if it's best for my project to use one (it's a small personal project). My issue lies in the fact that I can't think of anything for the BLL to do that the DAL can't already handle (executing queries and mapping results to objects), so my BLL just calls the DAL without doing anything itself.

Maybe I'm wrong about exactly what the DAL should be doing too. But regardless, what sorts of functionality should be expected of a BLL in a database management application?