OLY5 not all sleep traing involves crying, l never left my babies to babies cry. Not once.
You can edge young babies very gently and gradually into sleeping in their cot at a set time, without any distress, if you are willing to spend lots and lots of undisturbed time and effort doing it.
I have no idea about older babies and toddlers though.
I followed the Gina Ford plan from the beginning with my premie DD as l was pretty clueless about feeds/naps etc, and the message that if a baby is getting enough milk and the right amount of naps, during the daytime hours they will sleep for progressively longer stretches at night seemed sensible.
When l put my DD in her cot at night, from 3 weeks, l would feed, burp nappy change, lay her down in our semi dark bedroom in her cot, and initially keep my hand on her lightly, and make a shooshing noise.
she would wriggle, make little noises but never cried and would eventually fall asleep,
after a couple of weeks she fell asleep faster so l sat close but only lightly touched her,
Then a couple of weeks later sat v close, didn't touch her, but still made the SSH noises..when she was falling asleep almost straight away, l sat by the door and made the same shh noise.
Then stopped altogether and just sat by the door for a couple more weeks.
It took maybe 6 weeks or so.
From then on, I put her down and walked away and would watch/listen on the monitor and she would fall straight to sleep unaided. At 10.30 she would have a sleepy bottle and nappy change in the semi dark, and go right back to sleep till 5.30 ish.
When Ds arrived shortly after l did the same, but he took longer maybe 6 months to be as good as my DD at falling asleep.
Having a 22month old and a 6 month old who l could put in their cots at 7.30 pm and walk away from knowing they would soon fall asleep, was a lifesaver as l had no help as DH was mostly abroad with his job and no family were near.
It is possible to gently sleep train without crying or distress, but a lot of work......but then you have your evenings undisturbed, or to sleep yourself ( l used to go straight to sleep and set my alarm for the 10.30 feed!)