Everybody who will be at the table, including infants and non-eaters need to be included in the reservation because of fire code regulations. If you show up with extra people, the CMs will do their best to seat them, but there is always the possibility that anyone not included in the res will not be seated. If your extra person can't be seated and your whole group decides not to eat there, expect to be charged the $10 per person penalty. We were at a DW restaurant that was running far behind schedule so they were turning away walk ups, latecomers and anyone not on a reservation so it can happen.
If you have extra people and the restaurant will seat you, be prepared for a longer wait, especially if you require a larger sized table (e.g. going from 4 to 5 would require a 6 top instead of a 4 top.)
If you are an odd numbered group try adding 1 person. The online website has a glitch that makes it harder for odd numbered groups to find tables because a party of 5 typically will be seated at a 6 top, but the system wants to fill every seat at the table. If you make your party a group of 6, you might find more availability. When you get to the restaurant let the CMs at the podium know there are 5 of you. As long as at least one person shows up for the reservation you will not be charged for the "missing" person. The only time I would book for the exact number is for the pre-paid reservations such as CRT and the dinner shows since you'll be required to pay for everyone when you make the reservation.