Example use case :
If it is needed to choose a location, it can show the fields in this order : country -> state -> city where it will be multiple select lists of states that will show based on the country chosen. Same concept will apply for the city fields that will show based on the state chosen.
You can see the demo here :
-> search page http://demo.sobimarket.net/index.php/ssort?task=search&sid=40
-> add/edit entry page http://demo.sobimarket.net/index.php/component/sobipro/?task=entry.add&sid=40