SM: lots of things to respond to so I will do a bit of a nutshell response:
I always go by the behaviour of the baby. If they are already showing capability of sleeping through the night with no feeds needed, but are awakening a few times for the dummy or a chat or a squawk AND will not resettle without a parent's intervention AND the parents wish the baby to learn how to soothe themselves and go back to sleep THEN I sleep train. I don't let babies cry incessantly, I do let them chat and squawk and if they do cry it is only for a short time and NOT allowed to escalate into distressed crying. Much of the time if a baby does cry they are very tired and are asleep within minutes.
As for the feeding and growth spurts (whether at 4 months,9 months, etc), if a baby is eating lots during the day and is already NOT waking at night for food, then they are ny being deprived of any calories. If a baby does need feeding again at night then of course I feed them, I don't believe in depriving food. I don't go into the process of sleep training blind, I weigh up a lot of things including feeds, daytime naps, parents wishes, babies behaviour, what would be gained, what would be lost.... I sometimes tell parents their baby just isn't ready even if THEY want them to be.
I also encourage all parents who seek my advice to FIRSTLY think about what THEY want for their child. If what they want is a thing I can help with, then I do. If all they need is some encouragement to carry on as they are, as they have a routine that works for them, I'll happily do that too. I don't storm in like a sleep training Nazi, rather I aim to make sure the needs of the baby and her family all mesh together nicely, and what I do for one family might not work for another. I use my experience of many, many babies to find a solution that causes least upset but greatest satisfaction to the family. Some families are so sleep deprived and are so out of control that they are off the spectrum and you wouldn't believe the things they admit to wanting to do, including physical harm. In these cases a week of consistent support, a solid routine change, and a break for these parents might mean the difference between their child being harmed or not. I don't rush to SS about these families because I know I can help, however I have reported some families where other circumstances have come to light during my stay. So although many of you have quite harsh views on what I do, I can assure you I don't go into it lightly and I always have the welfare of the child as my number one concern.
I do feel some of you think I am cruel or harsh or depriving the baby of attention/food/whatever. I am not. I never do anything that the baby has not ALREADY shown some capability of achieving. The only exception to this is in families where things have spiralled out of control and then the baby usually responds quickly with 3 days to the new routine, and with minimal distress, as someone else pointed out: routine led babies sleep pretty well once they are on a routine that suits THEM. And their parents are so incredibly grateful. It's hard to understand just how desperate some parents are if you are happy yourself and doing something that works for you.
Sorry to waffle on, I just am upset at some of your views of me. Judgements are quickly made here it seems.