What's the difference between a lightweight hair oil and a heavy overnight treatment?

Lightweight oils and dry-oil sprays (like OGX's mist or argan serums marketed as 'weightless') are formulated to add shine and tame flyaways without leaving hair greasy, making them suitable for daytime and fine hair. Heavier treatments and bonding oils are typically applied to damp or dry ends, or left on overnight, to deeply condition coarse, dry, or damaged hair. Fine-haired users generally prefer lightweight formulas to avoid a flat, oily look.