The best things about the slings is that they are better for the baby than stroller. Children who are carried in a sling have to compensate for the mothers movements and shifting weight. The children grow up to be more agile and have better body control. (Think sports) They babies also are within their mothers communication area and often learn to speak and communicate better.
It is good for the mother two as it is cheap and can be used even up to two years old (if it is a strip of cloth) Helps the mother loose weight because she is carrying the weight that increases slowly over a period of time Finally some wraps make it possible to carry the baby low on the hips that prevents later back problems.
I used a strip of cotton cloth and knotted it on my shoulder. Later when the baby could sit up I kbnotted it across my chest and under my arms The baby rode my backside. (Think Africa)