Jim McKenna talks about how co-sleeping can reduce sleep apnea in a baby.
I don't think he's mentioned a benefit of co-sleeping that a friend of mine
noticed.

Her husband has sleep apnea.  She watched husband and daughter napping
together once.  Husband's breath caught and stopped.  The baby stirred
restlessly as the episode progressed, which caused her husband to stir and
start breathing again.  Neither one woke up.  Mutualism in action!

Diane Wiessinger, MS, IBCLC, LLLL  Ithaca, NY