The most common level of protection would include disposable gloves, lint-free paint coveralls (typically disposable), a cartridge-style respirator rated for the material being sprayed, and a full head covering sock. Especially nasty brews of paints may have requirements that exceed this level of protection, and may require full head-gear with a respiratory air supply. Precautions should be observed at all stages of paint handling, not simply while in the booth doing the actual spraying. This includes protection from contact and vapors during mixing.
Clearly, the health aspects here are the primary concern; however, there is also the consideration of minimizing the potential for contamination of the paintwork itself. Lint from street clothes, the oils from skin contact on the car's surface, or a stray hair or two can ruin the paint work in a hurry. Using the recommended protective gear will not only protect the paint applicator, but it will protect the paintwork at the same time.