I've never used TTO before, and I've heard some people use it just on their scalp? What does it really do to your hair?

Naturally brunette but dyed hair, dark brown ( nearly black ) in November 2010.Trying to grow to WL but only past SL atm. Currently not CO washing and using Pantenes shampoo. Styling: Schwarzkopf ultimate repair serum with total ends repair. Also use Aussies 3 miracle worker from time to time. 3B,bouncy ringlets,medium thickness,strands are neither fine nor coarse,dry,low elasticity ( when wet, but high elasticity when dry ) and proud to be a curly!