[paulsmith]

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/

[mulmen]

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

[paulsmith]

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