Strictly speaking, you don't "need" to, not the way that you need food and water. But safety clothing is designed to protect you from certain risks and dangers, so ignoring them will make you more...
Safety clothing is used to protect your skin, and body generally, from hazardous agents in the workplace that could damage your skin, or body generally.
Beekeepers wear protective clothing so they will not be stung. One or two stings is annoying and painful, but large numbers of stings can be fatal. When you are working around entire hives of bees,...
Light colors, like white or pink, reflect light and heat from the sun, making you cooler. Dark colors like black and brown absorb light and heat, so they make you hotter
For general attire you can wear anything you are comfortable with. In stricter moral or religious settings more and simpler clothing may be required by society. In dangerous settings you need...