Make the reservations, the days of walking up to a restaurant and getting a table are over; there are times when CS places have a 30-45 minute wait
It depends on when and what you want. We were just there from May 11th to 19th. Wait times at CS places were minimal to nonexistent. TS was no problem for what we wanted. Chefs de France for lunch (restaurant was almost empty), Artist Point for dinner, Tokyo Dining for lunch, California Grill for dinner, Cape May Cafe for character breakfast - all booked the morning of or night before. No problem for five (sometimes two people). At Studios one day every place was available for walk-up. Again, it depends on when you go and where you want to eat, I suppose, but the days of spontaneity at WDW aren't completely dead. Anytime we've walked up we've rarely been turned away.