You can certainly try experimenting with how your hair tolerates leaving oils in overnight. Some students have had great success with it, though it doesn't work for everyone. If you try it, please be sure to use oils that are friendly to your porosity type. Some people with scalps that are super sensitive to oils, may find that although the oil is only applied to the strands, throughout the night it does get on their scalp. This could cause them to see some increase in hair loss or irritation depending on the extent of their sensitivity.