My point is that it's never described. Even in the detailed options for those cookie banners that permit you to tweak things. Sure, there are (some) details about "our partners" and advertising etc, but exactly how the service will be improved is never explained.
The reason is simple and obvious: nobody knows. Companies collect data in the belief it will be useful in improving the service, but generally chuck it into a data-swamp and occasionally rake it over to extract basic info like navigation routes.
I'm also rarely convinced that improvements can't be better determined by focus groups and other similar methods.
"Improving our service" is a glib catch-all that rarely stands up to scrutiny.
There may be specific examples where a cookie is genuinely the best method to improve a feature -- in which case: name the feature, list the metrics, declare success/fail criteria, and stop collecting the cookie after the decision has been made.
