As a pediatric physical therapist, I always tell people
my job is to teach children to move so that they can explore and learn from their environment
What does this really mean? Take a baby who is seven months for example. Typically this baby should be rolling around their environment and getting into places where Mom and Dad don’t want them! In doing so, they touching different textures that they have not been able to get to, playing with the box that is on the floor, getting to new toys that they were not able to reach previously. As the baby touches the new toy, they learn about the properties of the new toy. Perhaps they put the box up to their mouth and yell into it and hear their voice echo back. Perhaps they put their hand inside and realize that it is a hole and something is inside of it. Perhaps they bang on bottom of the box and listen to the noise that it makes.
What if this baby does not roll, while the baby is able to play with toys that are near them if he or she can reach them, they are not able to learn and experience new things that are self motivated unless someone brings a new toy to them. Not every child that does not roll by seven months has a developmental problem, they just maybe lacked the proper exposure strengthen the muscles they need for rolling.
Therefore, effective exercises for baby from the start can strengthen the muscles necessry to help her to move so that she can explore and learn from her environment.