It's interesting to see research on this topic. It fits with what many people would instinctively feel - that infants need their mothers (or primary caregivers when the mother is not available).
Human infants are born neonate, extremely vulnerable and undeveloped compared to other primates. Because we walk upright, the pelvis has shifted, meaning babies have to be born before their skulls have fused, in order to fit through the birth canal. By comparison with our nearest relatives, adjusting for body size and brain size, humans should be pregnant for a year - it's called the missing fourth trimester.
This extreme vulnerability means babies really do need their mothers - and preferably it is the mother, as it's her voice, her body and her scent that even a newborn recognises. Sometimes the mother is not available but where she is, no-one should be artificially separating her from her baby, especially not overnight, which is the peak of vulnerability.
Sleeping in the same room as your baby reduces the risk of cot death - and yet some people mistakenly think it's OK for the baby to be handed over to someone else one night a week. That's adult-centred thinking, not baby-centred thinking.