For example, health care plans in the US are county-specific with regard to premiums, co-pays, etc. (based on demographics). Allowing someone to type in their ZIP Code to get started can be a better user experience than having them pick their county.

https://www.healthcare.gov/see-plans/

Except when it isn’t. I’d be curious to know the population in areas where a zip code spans multiple counties.

In that case, each county that corresponds to that ZIP Code is shown and the user can disambiguate manually.

Yeah it makes it easier. And I’m appreciative of the idea of making address entry easier for users but if they have to disambiguate did you actually make it easier?

I think Zillow does it best. You just type your address in a box and it looks up the normalized full address.

That makes everyone happy.