Data access layers make a lot of sense when many different parts of your application need to access data the same way.
It also makes sense when you need access the same data in many different ways. For example, how word processors can read many different file types and silently convert them into the application's internal format.
Keep in mind that a DAL can also be very counter productive. If you are building a system where data access performance is critical, separating it from the business logic can make some vital optimizations impossible.
