The problem with grinding them at the store is you vastly decrease the lifespan of the beans in terms of quality. Whole bean coffee, properly stored, can keep in the pantry for months. Once the coffee is ground, it starts losing its aromatic qualities within hours (even if you are storing it in an airtight, opaque container). It won't go stale or rancid that quickly, but there will be a noticeable drop in quality. So I really wouldn't recommend pre-grinding unless you go through the bag within a week.