A study shows us that a keyboard over 15 inches in size, could likely cause a long term health issue like scoliosis and spine pain to the long term users!
When we are using a standard size keyboard which is around 22 inches, our right shoulder will tend to be lower than our left shoulder always due to the keyboard layout. The space between mouse and the keys is too wide for our body to balance our shoulder. That causes a mussel disorder (or mussel adaption) when our shoulders are keeping on same tension for years.
To correct this problem, either the manufacturer change the size of the keyboard or we should buy a keyboard size under 15 inch.