The big word is underwear !
Anyway heres a joke "what's the difference between a man and a superman?" - man wears an underwear from inside while the superman wears it from outside.
I guess if you wear it or not its not much difference as you are not going to die. Our ancestors never have worn it nor any kind of living beings.
Generally when a child is send to school - its recommended to better to make him wear his underwear at the age of 6-7. Its better to be carefuly as its might probably stop infections.
Also its better to make him/her wear a better quality underwear (this is also recommended to adults) -- its better to go for soft underwear (as your body needs breathing or air) Its better to sleep without underwear on (as you are sleeping and there is zero chances of infection and you can sleep in piece without sweating from you waist ) This is important as the tightness of the underwear might block your blood flow from waist. Do regularly change your underwear.
Yes offcourse there are people who don't wear them and enjoy freedom!! - but some point of time they have to be a little careful
Infact basically underwears are available in varous flavour - truck , bikini kind of (side cuts ) - bikini / side cuts are a bit better as it allows more air. Nowadays designer underwears are also available - yes you can show them off in sea beaches to get noticed!!! -- so enjoy your underwear.