I may be rambling but...
I've watched youtubers that have used a dime or nickel sized amount for their hair. I watch them very closely as they are applying the product. What I have noticed is that they are just covering the top layer of their hair. So, I am thinking to myself, if most of your hair is not getting any of your product, why even apply it in the first place. It can't be making much of a difference if most of your hair is doing fine without it.
My hair needs product. I don't drown it, well except when I deep condition. I use a good amount when I am detangling and styling. I need that slip. When I am moisturizing daily, I use about a nickel to quarter size of each item (conditioner, olive oil, and wheatgerm oil). I get an even distribution throughout my hair by mixing them with water and using a spray bottle.