Actually the last patch has changed the funtionality of the swing. Pre patch 1.36 it was a motive mobile for infants and toddlers. Post patch 1.36 it only acts this way if you have it turned on so there is more interaction needed to make it work. However, it's exactly as ratchie says. The baby is taken care of very well in the swing plus it's small and only takes up about as much room as a highchair. And in game it's cheap as it only costs Sims §60 versus a couple of hundred for a crib.