Pick a city/town, without specifying an address
Sometimes you might not want to collect an address, but just a region where a responder is interested in or living. A good example would be if you're collecting information about where a responder might be looking to rent or buy a property, without knowing where exactly. That's what the region question is for!
Providing a Google Places API key will allow autocompleting the remainder of the address parts from the value that the responder types into the first field.
Most larger towns and cities in the United States have more than one corresponding ZIP code. Consequently, autocompleting a string like "brooklyn" is ambiguous when it comes to ZIP code.