The electronic trip gives you adjustable pickup and time-delay settings, which matters when you're coordinating downstream breakers and need to dial in the trip curve without swapping the whole unit.
The electronic trip unit inside the LE36400LS2103 is what separates this from a thermal-magnetic breaker. It gives you more precise long-time, short-time, and instantaneous pickup settings, plus ground-fault protection if the trip unit includes that function. For a field-service tech troubleshooting a nuisance trip: you can read the trip flags on the unit's face to see what caused it — overload, short, or ground fault — without dragging a scope into the panel.