PROS:
-Reduced risk for SIDS (this is particularly important in the early months, when SIDS is more of a risk)
-Better milk flow (particularly helpful for mothers who work outside the home - co-sleeping often helps these mothers to continue breastfeeding, when their milk would otherwise dry up)
-Often, both Parents and Baby sleep better, particularly when Baby is very young (under 9-months)
-Being close to Mother is usually comforting to Baby
-Parents don't have to leave their bed to feed Baby during the night (which results in less fragmented sleeping patterns for everyone)
-Parents and Baby have the chance to deepen their bond by sharing sleep together
CONS:
-Neither parent can consume alcohol or take any other drug that causes drowsiness
-With an older baby, there's less room in the bed (and you'd be surprised how much space that baby can take up!), and Baby may be a restless sleeper (kicking you, pulling the covers, etc.)
-Baby may have more fragmented sleep patterns while co-sleeping than she would in her own bed, resulting in over-tiredness, and eventually exhaustion
-Mother or Father may sleep less well with an infant in the bed, for fear of hurting him
-Baby may become so attached to Mother that she can only sleep with the breast in her mouth, or while lying on top of Mother (resulting, often, in poor sleep for Mother and possibly Baby, as well)
That's all I can think of for now. I am a strong advocate for co-sleeping, particularly for babies under 9-months. I think it's very helpful for many families, and is often a wonderful sleep solution. However, it doesn't work for every family (and you do need to take into consideration the needs of the entire family unit - not just those of your baby). Many people are very passionate about sleep solutions and sleep situations (both for and against co-sleeping, sleep training, etc.), and so you will find very thoughtful and well worded arguments for both sides. My motto is, it's important that everyone in the family gets a healthy amount of sleep, and the needs of each family are different. It doesn't matter if everyone's sharing one bed, or if everyone is sleeping in separate rooms: it matters that everyone is sleeping well. Lack of sleep is what will stunt your child's growth and development - not where he sleeps. If he's sleeping well in bed with you, by all means, continue that. If he sleeps better in his own bed, then that's where he needs to be. Flexibility is the trademark of a good parent, so if what you're doing isn't working (i.e., sleep isn't being had), try something else for a while to see how things go. Bear in mind, also, that your child's sleep needs may change as he grows. Perhaps your 3 m/o slept beautifully in bed with you, but your 1 y/o does better in the nursery with her older siblings. Maybe your first child needed his own bed right away, but your second child needed to co-sleep until age 5. Sleep needs and preferences are very individual. For every parent who swears by co-sleeping, there's another who swears it does more harm than good. Babies don't come with a personalized manual, so it's our job as parents to figure out their needs and do our best to meet them, and adapt as those needs change.