When you make your reservation, they will be very clear about what day you are checking out, so you aren't booking an extra night. I've done it myself, where I said I need a room 1/1-1/6, thinking those were the nights I needed, but check out is 1/7. The folks on the phone always clarify and make sure the dates are correct for what you need. (They must be used to confused people like me!!!)
Also, if you sign up for the dining plan, you can use the meals on the day you check out, so it's like an extra day if you are in the area...