As far as I know it’s just some additional, more fine tuned, calculations you could use in a theme or theme component. But they are not used in Discourse core.
If you’d want to write your color scheme with just the numbered values, you could re-declare the descriptive ones like that in your theme:
:root {
--primary-high: var(--primary-800);
}
But then, there’s only numbered values for primary and tertiary.