If you really want to go to a particular place to eat then it is always best to book. I think nowadays it is alway best to - you can always cancel with guest services if you decide not to go so the table will be available for someone else.
We booked Le Cellier last year and they were turning people away - also at CP in the MK and at the CG at the CR. I would imagine you can still get some walk ups - we did at the Plaza Cafe in MK but there were only 3 of us.
Good luck with whatever you decide
