It also forms a protective barrier for your skin, so nothing can contaminate it or grow on it and you don’t lose moisture to evaporation.

Also, pores don’t actually clog from stuff getting into them. That’s a common misconception that mostly comes from advertisements. What actually happens is your skin becomes inflamed (due to contaminants or bacterial growth or diet or hormones) and squeezes the pores shut. Blackheads aren’t dirt but are actually oxidized sebum, which is the oil your skin secretes.

EDIT Oh! Speaking of protective barriers, I also put it on my hands and forearms before work because I handle a lot of machine oil and that irritates my skin, causing rashes and itchiness.