Protective clothing is a feature of a number of activities. Athletes wear cups, scientists wear goggles, construction workers wear hard hats, and other workers wear work gloves and thick aprons. Protective clothing is often uncomfortable for workers and expensive for employers, but a number of reasons necessitate the use of specialised gear.
The most obvious reason for protective clothing is safety. If you're running a chainsaw and wood splinters are flying in all directions, you'll need glasses that protect your eyes and a heavy jacket that stops wood splinters from cutting or piercing your skin. The same goes for safety equipment in other situations; certain clothing items protect workers from job hazards.
From an employer's standpoint, the safer workers are, the fewer injuries will occur. And the fewer injuries that take place, the steadier production will be. Of course if production remains steady and employees stay safe, then it will stabilise output for the employer, making the company more reliable.
If an employee is injured, then the insurance company can deny coverage if he wasn't following safety procedures. If company safety procedures detail certain protective clothing as a safety procedure, then an injured employee may be stuck with his injuries and medical expenses without help because he didn't wear protective clothing.
Another benefit of protective clothing is that it identifies workers in a given area. A lab coat could be considered protective clothing in a chemical lab, and individuals wearing lab coats can be identified as chemists or people working with chemicals. In the same way, individuals who wear hard hats on or around a construction site may be identified as part of that site's work crew.
Wearing protective clothing ultimately saves money. It keeps the workers safe, and as such they don't lose wages from injuries. The employers don't lose time for workers being out, and insurance doesn't have to pay for workers' compensation.