We eat at CP every trip, including our visit two weeks ago. We never make reservations in advance. When we enter MK in the morning, I go right to CP and make lunch reservations. Prime time, around noon, is generally booked, but we never have trouble getting a late time like after 2pm. So we just have a snack mid-morning and then a late lunch. There is just no way for us to know 3 months in advance what park we will visit on what day.
So if you must eat lunch at a certain time, book in advance, but if your schedule is flexible you'll be fine without advance booking.