People with oily skins are the ones that mostly suffer pimple problems than less oily skins. Because of this, they tend to avoid oiling their skin to keep it as dry as possible with acids and over cleansing which is a problem also.
However, there are benefits of using oil on oily skin:
Oiling the skin prevents the skin from overproducing oil.In an effort to combat pimples, people tend to dry out their skin too much with acids and over cleansing, which allows skin to overproduce oil (even more than normal for oily skin) and breakout.
An over production of sebum causes oily skin, which yields varying amounts of acne.
Oils like mineral oil actually dissolve other oils in effort to keep the face cleansed and hydrated. Some skin moisturizers help in keeping a balance. People with other skin types can also explore this process.
Oily skin is caused by sebum, the substance that is secreted from sebaceous glands and is healthy in nourishing the skin in normal amounts.