The drains of your plumbing configuration are extremely important to the overall function of the system. After all, with a drain in your shower, the water, soap, and strands of hair would simply fall through a hole in the floor and collect under your house.
The trouble is, if something goes wrong with your drain system, the result is a collection of all of those materials flooding out of the drain and into the floor of the shower.
Either way - it is essential to the health and well-being of your household and your home to have a properly working drain system.