DH is rather older than 6 mths.
He has been away for work today and is likely to get back quite late - after midnight. He will have had a beer and possibly a cup of coffee and a sandwich on the train. I know he won't be dehydrated or hungry because he will have had breakfast, a big lunch, snacks and that sandwich. So when he comes in, and boils the kettle or goes to the fridge for a coke, ready to sit on the sofa and chill for a short while, I will be quite firm and tell him he doesn't 'need' anything to drink or eat. I'll tell him he is having the tea/coke 'just for comfort' and he should learn not to bother. If he wants to greet me with a kiss and cuddle, I'll tell him the same, shall I?
We expect a huge amount from our tiny babies if we think that their through-the-night needs for comfort should be ignored because nutritionally-speaking, they should learn to have their calories in the day...and that they have to learn that lesson by being so distressed they cry and scream indefinitely, only to be ignored.
What's that saying to them? 'No matter how upset you are, your wish for comfort and closeness and milk will not be met by the people you love'.
'Cry it out' does of course work in time - at a price. If I continually ignore or belittle DH's wish for comfort, or if he continually ignores or belittles mine, then in the end the requests go away - and the needs are buried. That is not good for anyone's relationship - partners, parents, anyone's.