I had a whole post and then my phone dropped the webs. Been doing that a pst lately, but I digress.
What do you think when you hear CIO? Baby left to scream for hours no matter what? What is their definition of CIO? My baby will not drift off peacefully being rocked sucking on her bottle. She needs to be tucked into her crib and she protests for maybe 5 minutes, then she's conked. If she is disturbed, she thinks it is playtime. If she is revving up or does not stop after 5 minutes, I see if there is a fixable problem (she threw her paci out of the crib) and if not, I get her up and try again later.
Honestly, I had thought she was "high needs", but one evening I had to put her down to deal with her brother and by the time I was done with him, she was fast asleep. Tried it again the next night and same thing. Bedtime "routine" went from 3 hours and about to scream to 45 minutes and all getting to bed at a decent time (45 minutes is bath, diaper change and jammies, a snack of yogurt and fruit, bottle of milk, rocking a bit while drinking the milk, then tuck in and asleep within 5 minutes. I have 2 other children, a dog and a cat I'm wrangling during that time, too, though 1 child is pretty self-sufficient.). If she wakes in the middle of the night, I confess I try to wait a moment to see if she just falls back to sleep--or DH will get up, but I end up stumbling to her and giving her her midnight snack bottle.
ETA: Had she been my first, I would probably be one of those "just let baby CIO. It works!" moms. My older two--no way, not no how. If they were to be tucked into their cribs and left to fuss it out, they'd scream for hours. They both ended up cosleeping for years.