Yes, remapping a car's engine control unit (ECU) can improve fuel economy and reduce emissions:
Fuel injection and ignition: ECU remapping can optimize fuel injection and ignition timing to improve combustion and fuel efficiency.
Airflow and sensors: ECU remapping can manage airflow and sensors to maximize fuel efficiency.
Engine responsiveness: A more responsive engine can make overtaking easier, which means fewer gear changes and less fuel consumption.
Driving style: If you're heavy on the accelerator, remapping won't improve fuel economy.

No, engine remapping typically doesn't shorten a car's engine life. In fact, it can sometimes improve a vehicle's lifespan by increasing power and performance. However, how the car is driven and maintained is what ultimately determines how long the engine will last.

Yes, remapping a car usually voids the warranty, but there are some exceptions:
Manufacturer policy
Most car warranties state that any modification to a car's components that is not approved by the manufacturer will void the warranty.
Manufacturer discretion
Some manufacturers may only cancel certain parts or systems that were impacted by the remapping.