I've been wondering about this question for a while as well. I use a mix of coconut and olive oil as a pre-treatment every time before I wash my hair. It's supposed to prevent my hair from swelling too much while I'm washing it. But can the oil penetrate into the cortex of my hair at all if I have used a leave-in conditioner that contains amodimethicones after the last washing or is it completely useless then?