First and foremost: Children are the product of what they themselves bring to the table and what the environment does to them. The former is important, because essentially it says: Every single child is different. What works with one child might fail with the next one. Keep this in mind and remember that you will have to find out for yourself. _For each of your children.:
That said, in my experience repeated routines make it much easier for parents. Within a few months, the child will develop a certain rhythm that you can (somewhat) depend on. It is a very good thing when you "know" that your child will fall asleep about an hour after breakfast and sleep about until 11:30am. This gives a world back some of the sanity you took for granted before you became a parent.
On the other hand, repeated routines make your child (and yourselves) inflexible. That is, it will be hard to go visiting someone (or even just have someone visiting), because the child will be overexcited by the changed routine/environment, spoiling the visit. If you find yourself trying to function like a clockwork, you might raise a child that only "functions" in a clockwork-like environment. Most parents, however, want their children to be able to stay over at the grandparents', to be able to stay up a bit longer when they're at their best friend's birthday part, to sleep half an hour longer the next morning, to move their cycle to a later schedule during a vacation, and move it back afterwards. A child that has been put to bed at 7pm for 27 months in a row will usually react badly to any such events.
What the balance is depends on your child and on its parents. How much can this child take? How much energy do you as a parent have to deal with a tired child? Are you someone who, when you collapse beside your child at 10:30, regrets the whole idea of going to that birthday party or will you inwardly smile and consider the nice evening well worth the trouble? The more you can do the latter, the easier it will be for the child. ("A child won't feel well if its parents don't.") So here's my rule of thumb:
Do as much routine as you find necessary for the child's and your own wellbeing. Do as little routine as the child and you can deal with.
If in doubt, err to the side of less routine. Your child can deal with it (our ancestors didn't roam the African Savannah with a clock in their hands and had different excitements every day), and you will likely appreciate the resulting higher flexibility later.