I had my first baby at 18 and still took a lot of 'advice' from my mother, who was nuts. She was one of eight kids and her younger brother had fallen from his high chair and banged his head. Although my granny had him checked thoroughly and pronounced fine, my uncle had in fact sustained a tiny fracture on his skull. He cried a lot after that, and it greatly distressed granny, who already had three older dcs under the age of six. She knew something was wrong, but felt nobody would listen, until my uncle developed meningitus on the brain, thought to have been caused/associated with the fracture. He recovered but it left a lasting legacy in the family.
It was completely unacceptable to let the baby cry, ever. This was passed on to me by my mum, and although I agree in principle, it meant that I was completely unsupported when I wanted to implement some kind of routine with my first ds. In fact she'd go in and pick him up from his cot if I put him down and he cried. He was five years old before he went to bed alone, and to be honest at that point I was nearly deranged due to having zero personal time without him, and being forced to lie down next to him every night for hours while he fell asleep. To this day (he's 18 now) I feel it's negatively impacted on our relationship and also his sleep patterns. He literally never got left to cry. Ever.
My 2nd and 3rd ds are twins. I had them when ds1 was eight, and by then I had escaped my mothers clutches. I certainly never planned on leaving them to cry, but as I lived in an upstairs flat, was a single parent and had the school run to do with elder ds from day one, there were times when I'd be loading babies into the pram, and one or the other would be howling. Nothing I could possible do if we are trying to get out the door, and I knew they'd been bf all through the night and early hours, then washed and changed. They just were tired and being forced into coats etc and stuffed into the pram. Often I'd put one baby in the pram, who's start to cry as I ran back up for the next baby. By the time I returned (two minutes later) the baby would be asleep.
I did cc when they were 11 months old. I stood just outside the bedroom (still co-sleeping at this point) and rapid returned them if they crawled to the edge of my double bed (with banks of pillows on the floor in case they fell, which they never did) It took a few weeks. They are nine now and have amazing sleeping patterns, go to bed very nicely and sleep through perfectly.
I discussed this with a HV. I know some HV are rubbish, but I thought she had an interesting point. She said, that if baby's needs are constantly and perfectly met (we were talking about the older baby, six months plus) then that baby would not develop any coping mechanisms for handling stress.
Whether that's true or not, I don't know, but I do know of the three children, my eldest copes the least well in stressful situations. The younger two, who are very different to each other, certainly manage it better.