Trips work with total counters from the car. This means that the start of a trip is a bookmark, you only need to run the app when you want to start (or reset) a trip. After that the app does not need to be running, until you want to read your trip stats.
*Note for Model 3: Model 3 only sends Odometer when the car is 'on', after pressing the brake pedal. So in order for a trip starting point to be stored properly, you need to have your trip tab open, and the car must be on at the same time. You can tell by seeing the 'distance' signal is showing. If not, do a 'reset trip' from the menu with the car 'on'.
You can delete any trip with Menu arrow - Delete tab.
For model S and X, please note that trips in this app differs from the Tesla on-screen trips by that it also counts standby/parked battery usage/losses.
For model 3, the counters should match what the car reports, except we've tried to add the standby losses as a separate reading ('Stationary').
This behaviour is different because the cars have different sets of data available to us on the CAN-bus.