Our spines have normal front-to-back curves: forward-facing curves in the neck & low back, and a backward-facing upper back curve.
But “sideways” curves in the spine, called scoliotic curves, aka "scoliosis," those that you would see if the person has their back to you, are abnormal and can cause trouble. They have the effect of weakening the stability of the spine, which affects the attached and related soft tissue, including muscles and organs.
Severe or advanced scoliosis can impair the lungs & breathing, as well as the functioning of other essential internal organs, and may require surgical stabilization.
In my practice, I have worked with scoliosis patients who have successfully chosen to avoid surgery, and instead relied on consistent, regular, specific exercises and regular chiropractic care to manage the effects of their abnormal spinal curve(s).