Shampoo belongs at the roots, care in the lengths.
Dirt and sebum sit on the scalp, so that is where you wash. The lengths get enough of it while you rinse. Massaging shampoo into the ends dries out exactly the part that can take it least.
The same holds the other way round: conditioner and treatment belong from about ear height downwards. At the roots they make the hair heavy and the scalp greasy sooner.