I have baby sat for a young baby twice, once at 5 weeks old, once at about 8 weeks old. I refused to do so after that even though it caused 'big problems'.
I refused because it was the most horrendous few hours I have ever spent (and like most older people I have had a few of those). I literally could not have done it a third time, it was like being tortured.
The mother of the couple told me that the baby had to be put to bed by such and such a time, and then I was not to go into see the baby after that, that "they" left it to cry. The father didn't say anything. I was told that the baby would cry for about an hour before it fell asleep, and it did. My every instinct told me to go to the baby, pick it up, cuddle it, check if it needed a nappy change etc and that it hadn't been sick, or have a temperature etc. But I was pretty sure that it only needed comforting.
By the way, it was in it's own room by then, the mother tried having it in the same room as her for a few weeks, but couldn't hack it any longer - I suppose it was more difficult to ignore the crying if the baby was in the same room.
I actually wanted to report them to the SS, what stopped me was that the mother appeared to have PND, but she wouldn't tell anyone else about her difficulties. But apart from fact that I never saw the mum ever cuddling her baby, and we were only allowed very short cuddles while we gave the baby it's bottle, then it either went in it's cot or one of those bouncy chairs, the baby was putting on an adequate amount of weight, it was bathed, it did wear mainly clean clothes. Dad appeared to not be allowed to do much for the baby except change it's nappies, and the mum moaned at him if he took too long, ie gave it a good clean and applied nappy cream.
Reading this back now, and seeing the child as they are now - nearly into double figures - but completely besotted with it's mother more than any other child I have ever known - they only want to be with their mum, they always behave for their mum, but they play up a lot when their mum isn't there. The mum still palms the child off as much as possible, but there are still very strict rules for anyone looking after the child.
I am very concerned that I made the wrong decision when the child was a baby, but I have heard such awful things about the SS, and about children who go into the care system that I was scared that that would be the wrong decision too. Also I knew the father was there and would stop the mother if she ever got violent with the child - having said that, he did work, and she didn't.
Anyway, that is what being left to "cry it out" means to me, and I could never condone that.