Did CC at around 8.5mo as DS was waking every hour in the night, usually being awake for two hours in one of those periods (with DH or me rocking him constantly). After 3.5mo of that (and before that, the best was two wakes at night for BF and first three months little sleep at all) DH and I were broken. We got DS checked out by the GP and a cranial osteopath. Both said seemed to be DS had a habit as no problems they could find.
We did CC, and it worked until DS got a cold about 3 days later. We tried again when he had a break in teething/colds at around 10.5mo. And then again at around 13mo. And then again at around 15mo. Finally we seem to have helped DS settle back to sleep unless he needs us to do something.
But still he only sleeps a bare 10 hours at night and about 75mins during the day.
I appreciate those who have said they never have, but that they can see why others with more challenges felt they had to.
And to those who think CC is about leaving a child in pain/hunger, you really need to read Ferber's book, as this is not what he advocates. The opposite in fact.
DH looked into all the research that the anti-CCers rely on, and frankly it's not definitive. Because nobody would experiment on small children.
We do our best as parents.