I don't believe it's necessary Min, but a lot of people do it. We stopped wrapping Jacob at around 4w of age as he seemed to prefer having his arms out. He would be tucked in quite firmly though and made sure that he had enough clothing and blankets on him to keep him warm.

Some babies do however find comfort in being wrapped, and it's often something that is suggested to try if your baby is unsettled, as they can find it soothing.