Substitution replaces a word or phrase with a shorter pointer.
Replace, don't repeat
I lost my old phone, so I bought a new one.
Pointer words
one/ones, do so / do it / do that, so/not, that/those, such. Ellipsis leaves a gap. Substitution fills it with a small word.
I want the red car, not the blue car. — heavy
I want the red car, not the blue one. — yes