Having a newborn at home can be nerve racking business. New moms are notorious for worrying about every possible thing, and tracking their baby's progress like it's their job (because, well, it is). It can be hard to differentiate between healthy progress and worrisome delays when your baby is so small, so learning the true developmental milestones they should be hitting at each month will give you less to worry about. Similarly, knowing any newborn red flags when it comes to their basic development can give you some guidance when you're deciding whether or not to call the doctor.
I remember worrying about every little thing when I had my first daughter. She hated tummy time, so I worried her head control wouldn't be on track. I watched her eyes obsessively, making sure they tracked movement and reacted to bright lights. Knowing the range of "normal" ahead of time would have saved me a lot of worry and allowed me to simply enjoy the short newborn period even more.
Keep in mind that babies all develop at their own pace. But these guidelines are meant to act as just that, guides to give moms a sense of what is normal and what is worrisome when it comes to their baby.