> Conclusions The intervention improved caregivers' assessments of infant sleep problem severity and parental depression, fatigue, sleep, and sleep cognitions compared with controls.
This is largely true for myself - sleep training is for the parents to get some semblance of their lives back.
The first 3 months of my daughter's life - i'd never been more tired in my life.
See the co-sleeping debate is never ending and highly dependant on family genetics but the statistics referenced above are related to the parents' perception and well-being and not the cognitive development and well-being of the infants themselves.
However my views are based on the economic/societal/parental expectations in (progressive) North America and it’s certainly different elsewhere.
Edit: Added specificity