It depends, if you're going through quarantine/international you sometimes have to pick up your bags and then re-check them.
For example, flying SYD to SFO via LAX.
The US does not have the concept of international transit lounges like other countries do, where you can get off plane 1 and sit in a room that is not technically inside the country (so you don't clear customs or immigration), then just get on plane 2 and go to another country.
I suspect there would be cases where it's cheaper to book a connecting flight through the US to some other country (or US city) and just get off at your first stop.