Or is it about ensuring that mom and dad don't make a sibling that takes away the baby's resources?
Having run the same gamut three times, the best advice I ever got was: chunk sleep. Let the wife sleep for 4 straight hours, and then tag out, where the awake person sleeps if/when they can. I know nursing can gum this up, but either pumping, or just doing the formula thing, it's worth it.
It did! But we, in our infinite wisdom, got selfish and we now live alone. Fight nature and she fights back!
Somebody invented the crib, got rich at our expense, and now people can't imagine life any other way.
"It's very safe to sleep with your baby unless you sleep with your baby drunk or on a small couch", and
"It's very dangerous to sleep with your baby especially if you sleep with your baby drunk or on a small couch"
That last bit is right and a study found "The risk associated with being found in the parental bed was not significant for older infants (>14 weeks) or for infants of parents who did not smoke and became non-significant after adjustment for recent maternal alcohol consumption..."
See
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC28288/
Anyone who has shared a bed with a cat or small dog would note that you never roll over and crush it.
And the tradeoff makes sense -- as a parent, you are biologically programmed to go through great lengths to keep your children safe.
You mean Socially programmed.
Instincts are biological programming.
Parent under drugs/medications (including smoking) is mainly what drove the death statistics in cosleeping.
Don't have links to studies but is what is teached in official parental education courses in spain atm.
We co-slept for the first 2-3 months, then had baby in a "next-to-me" for a few months, then moved baby to a crib in his own room at 6.5 months. Prior to being in their own room, the baby would usually wake up every 2-4 hours, with the very occasional 6-7 hour stretch. After going in his own room, his sleep began to consolidate and he would regularly last from 7-8pm to 4am without needing resettling.
We have friends with a 4 year old daughter who co-slept until now and have just moved her to her own room. She wakes up screaming and needing attention most nights around midnight.