I've noticed that if I go without it, my skin is always dry no matter what. It's like it can't retain enough water or oils on its own. I use a mild surfactant to wash my face once a day.
It seems 100 years ago everyone had great skin and used nothing (at least men that is). You never see a picture of someone in the 1930s with acne, eczema, dry skin or inflamed skin. There was no such thing as "sensitive skin" products because no one had allergic or inflammatory reactions to beauty products.