This seems to be something that is widely disagreed upon by dermatologists and aesteticians...I have had derms tell me it doesn't matter what you put on your face, its your internal hormones and genes that determine how much oil you will put out. I have had derms tell me, your skin's oil COULD be effected by environment and most aesteticians swear up and down that outside stuff and climate causes more or less oil production. I have read that if you have oily skin you should not use moisturizer unless you feel dry, but have also read that you should always use it whether your skin is oily or not.
Does anyone have any advice on whether oily skin can indeed benefit from moisturizer? I live in a dry climate and my skin always feels pretty oily.
I have very very oily skin and also acne prone skin. For the longest time I never saw the need in using moisturizer because my face was already shiny in the first place. When I started getting acne when I was around 12-13 years old I started trying out all these acne clearing washes, toners and creams, my acne never responded to it though and it progressively got worse. My aunt who is a doctor, although she is in no way a dermatologist, explained to me that treating my skin with all there acne fighting solutions to dry out my acne just makes my skin worse because although after applying acne treatment your skin dries out, it then tells whatever oil glands you have in your face to produce more oil to make up for the dryness.
I started using gentler face washes after than and tried lightly moisturizing my skin and I did feel it helped with the oil control. Also, I keep my washing at twice a day and also use those oil control sheets throughout the day just to take away the shine from the face.
nicmac62 is right.
Moisturizer only helps oily skin if your skin produces more oil because of the products you use to wash your face.
But if you don't use products that strip the oil from your face that makes it dry then moisturizer won't help oily skin. (But personally I would still use it)
The more harsher the products, the more your skin will become dry which causes it to produce more oil 
Even if you don't use harsh stuff on your face i'd still moisturize at night at least 
cause it helps prevent wrinkles!!
Since you use Differin, I would moisturizer morning and night though. It dries out your skin.
PS: Milk of Magnesium helps for oily skin, it's weird but it works.
I recommend a light moisturizer even if you have oily skin. If you're using very stripping ingredients like benzyl peroxide you need to help your skin protect itself- essential you are removing the skins natural barrier and altering its pH- something that in itself can contribute to acne. Try to limit cleansing to once a day, evening is preferable. Then in the morning just rinse with water and/or a toner and follow with your normal routine.
Also consider your diet and the oils and fats you are consuming. Consuming fat is incredibly beneficial to the skin but only if it is the right kind. I recommend coconut oil and olive oil. Limit processed foods. We are what we eat- literally, the fat we consume becomes the fat and oil our skin creates. Processed, hydrogenated oils in the diet will come out in the skin.
Best of luck!