There are numberous applications for an API that can be used to create graphical depictions of the United States. National elections could use the API to create a map that will show which states voted for Republicans and which states voted for Democrats. CDC could use the API's to create maps identifying which states have been subjected to an infectous disease.
One of my personal goals is to visit every state in the United States. I used the API to create a graphical representation of states that I have visited so far. I could have used the color gradient to differentiate how much TIME I've spent in a given state i.e. I grew up in New Jersey, lived in California for 6 years, and lived in Georgia for 10 years so I could have made those states dark red and all of the other states a yellow color to indicate that I have not spent as much time there.
I could have expanded this to show countries I've visited throughout the world but I would not have been able to show the details of each individual state I've been to. I also could have "drilled down" to different addresses I've lived at but I did not want to show that level of detail.
I could also use the images created by the Google API in a document for work i.e. presentation. The URL for these API's were a little clunky to write as I had to include all of the state abbreviations and the color gradient required for the state.
This is a Google Map I've created to visually display the States that I have visited throughout the USA.