Nude Healthfulness
Although there are certainly times when some sort of clothing is truly beneficial and healthful (to protect from hazardous substances, to protect from extreme cold, to protect from extreme heat, etc.), I believe being nude is how our bodies were designed to function best.
Balls need to be about two degrees Fahrenheit (about one degree Celsius) lower than body temperature to produce healthy, living, viable, sperm. The bag in which balls hang is designed to stretch out and tighten up in order to regulate their temperature. Clothing tends to hamper that temperature regulation. The more restrictive the clothing, the more likely the bag will not be able to do its job properly.
Our bodies have an excellent cooling system that also works best when we are nude. Sweat glands excrete water into the surface of our skin. Evaporative cooling reduces body temperature. Clothing renders that system ineffective.
Foot fungus requires a warm, dark, moist environment in order to live and thrive. Shoes and socks provide that exact environment -- almost as if their true purpose were to promote foot fungus. Someone who rarely, if ever, wears shoes has essentially no concern about foot fungus.
Having you body open to free air exchange (sans clothing) greatly reduces the possibility of fungal skin infections anywhere/everywhere on your body.
Vitamin D is synthesized right on the surface of our skin in the presence of ultraviolet light. Given adequate sun exposure, skin will synthesize approximately 1,000 IU of vitamin D per minute for up to twenty minutes -- 20,000 IU of vitamin D per day. Skin color influences the rate at which vitamin D is synthesized -- lighter faster; darker slower. Clothing prevents vitamin D synthesis. The majority of the US population routinely wears clothing when out of doors; the majority of the US population is vitamin D deficient. This is a causal relationship.
Getting your full amount of vitamin D each day results in a stronger immune system and stronger bones. Vitamin D regulates over three-hundred processes in your body.
Seeing yourself and others nude promotes a better more healthful body image.
What can you add to this list?
I do agree 100% with this. When I must mow my lawn and gave to wear shorts (due to some people around, specially if minor are present) I do get really hot, to the point that I go into my back yard were I can remove the short and cool down as my testicles gets air, in a matter of a couple of minutes, I am cool and comfortable to continue with the mowing, so get my shot in and to the front I go. Most of the time I do it fully nude, since here in Florida is not illegal to be nude in your property, but when textiles are crossing the street of my house, I don't want to impose my way of life to anyone!
Its a proven fact also sleeping nude promotes more restful sleep. Clothing of any sort loose or otherwise can become twisted and tight to restrict blood flow, pinch nerves under the skin etc.
Also as you mentioned about temp regulation of the testicles, wearing underwear also during sleep restricts the cooling process. Testicles are most active when we are sleeping.