As you might already know, playing white noise for a baby is meant to stimulate the sounds of the womb (which can be deafeningly loud). This loudness is not abnormal for an infant, so the noise might make your infant feel more at home.
White noise acts as a sleep aid. It is relatively inexpensive and can be used to encourage sleep at all times of the day. This could be the result of white noise reducing stress, encouraging less crying. Some doctors even believe that playing white noise could lead to a reduced risk of a child experiencing SIDS.