Cuticles are a part of your skin that is located at the base of your nail. They act as a protective barrier over the growth matrix where the nail plate grows from. Cutting a cuticle is in fact cutting skin and in effect breaks the barrier or seal that protects the nails growth center. As a result, an open wound is produced allowing for exposure to germs that may lead to an infection.
When this happens, it causes a condition called paronychia where the area becomes red, painful and swollen. If this occurs, medical treatment may be required involving antibiotics and possibly draining or removing the nail plate. In many states this practice is illegal for salons to do or use credo blades at all.
If you prefer the look if tapered cuticles, a safer technique is using a sterile blunt instrument to have the cuticles pushed back instead.