It's just aesthetic. Heavy sun exposure throughout life leads to wrinkles and sun spots/splotchy skin later in life. White collar workers likely needn't worry, though. That advice is more for people who spend their working hours in the sun.
Have to disagree with this one, everyone who can't escape sunlight and likes to go outside at all is affected. People in the American southwest from all walks of life age shockingly faster (in appearance) than their northern state counterparts. I'd meet women who were 25 and looked 35 (by northern expectations), and it only accelerates from there (35 looking like 50, 50 looking like 70).