The ability to export and import sensors, gives you the ability to very easily copy sensor configurations between machines. For instance if you have two identical machines, both with twenty identical sensors, you can configure the sensors for one machine and then simply export those configurations in a single JSON file and import it for the other machine.
To do this for all the sensors associated with a machine, go to the sensor list page for that machine and click on the 'Import/export' button in the top right. Then select 'export sensor list' and save the JSON file somewhere on your device. Then go to the sensor list page for the other machine, click the 'Import/export' button and select 'Import sensor(s)'. This opens a page where you can either browse for or drag and drop the JSON file to import it.
This process can also be done for individual sensors by clicking on the menu option for a particular sensor and selecting 'Export sensor'. This also generates a JSON file which can be imported the same way as explained above.