Skin-to-skin contact or close proximity can regulate an infant’s body temperature and reduce stress hormones like cortisol in both the mother and the baby.
Most reputable articles on this topic emphasize the distinction between "co-sleeping" (being in the same room) and "bed-sharing," providing guidelines from organizations like the AAP to prevent SIDS while still maintaining the benefits of proximity.
The phrase appears to be related to a specific online article, though it could refer to a few different contexts.