That's is kind of like asking ... What does a doctor need to know about the body in order to treat it?
A nail artist is enhancing a living growing thing ... and what she/he attaches to this living growing thing is permanent unless removed.
The implications of that are enormous.
We need to understand growth pattern of nails and what affects it. (physiology)
We need to know how we can cause damage to the structure and therefore how to avoid doing so by understanding the structure of the natural nail. (anatomy)
We need to know what internal and external factors may be affecting the service we give to our clients - diet, general health, medication, stress etc.
We need to understand how the service we give can promote nail disease if we are not very careful.
We often are required to solve a problem for a client - how can we do so without any intelligence behind our thought process?
These are just a few reasons why a thorough understanding of nail structure, product chemistry, and the physiology of the nail unit are important in order to class ourselves as true professionals with a responsibility to our clients to look after and care for their nails and to keep them healthy.
There is a whole lot more to being a great nail artist and running a successful business than just producing pretty nails on the ends of someone's fingers.