Many people will tell you that using a sound machine with newborns is important for mimicking the sound of a mother's womb, the rush of the amniotic fluid surrounding the baby. And that may be true. It is certainly soothing for a newborn to hear the rushing noise they are used to. However, as a first time mom I didn't use a sound machine. Even with my second baby I didn't use a sound machine. They turned out fine and learned to sleep beautifully both by 4-5 months.
So why did I start using a sound machine when they were 3 & 4 years old? They share a room and as they got older, became more independent as all children do. They began wondering what we were doing downstairs after bedtime. They slowly realized they were missing out on the other activities after 7:00 PM. They weren't told that this was the reason we started using it, but the sound machine really helped us with FOMO (fear of missing out)!!! Once we made it part of our nightly routine to turn out Hatch Rest on, they quickly got attached to it. Perhaps the sound of the sound machine was soothing to them even if it was foreign to them at first. I explained gently that I didn't want to accidentally wake them up in the hallway so it was good to have this on. Now, they request it every single night and it is part of our life!
Needless to say, the sound machine isn't life or death with newborns, and it can be implemented later on, too. It won't ruin a child to use it from day 1, and it won't ruin them not to! Falling asleep to the natural sounds of the house you live in, nature or traffic outside, or even other siblings making noise in the room next door - are all heatly and normal. But if you have other comittments or other children to deal with, it can't hurt to drown out the noise and let your young children maximize the sleep they truly need.