Most people like to wear tight clothes to look attractive, younger, slim, and or stunning, without considering the effects of such dressing on their health, even when they have discomfort wearing those clothes.
There’s been some suggestion that tight underwear can cause low sperm count because testicles get too hot to allow the sperm to mature.
G-string underwear can cause skin irritation, as well as infections.
The friction from pants that are too tight, or pants that are badly stitched can cause genital irritation, and lead to infections.
In women, wearing tight pants can lead to overheating of the privates which could increase the risk of urinary tract infections (UTI) and yeast infections.