1. If I know in advance what ingredients I will need for family favorites, I can watch for low prices in the weeks prior to Christmas instead of just waiting until the last minute to pay what is likely to be a higher price at the last minute.
2. If I have a list to shop from, I am not as likely to buy a bunch of extra stuff on impulse just because it looks good.
3. I am not wasting gas and time running back and forth to the store for last-minute ingredients.
4. I do not wind up wandering through the bakery and deli departments at the last minute with a willingness to pay anything just to have something special to take to the party.