Honestly, I think a lot depends on your relationship with food. For those who haven't had huge issues with food like binge eating and food obsessions, I think it's totally realistic to go by instinct. But for those of us who have food issues, more structure might be better. I know for myself, who have had binge eating issues for years, I fail every time I try to eat by instinct. I get anxious if I don't know what my meals are going to be and even more food obsessed since I'm always going over in my mind what I'm going to prepare for the next meal and eventually end up going for junk food because it takes no planning.
However, when I plan out my meals, I do a lot better.