Essentially, an ECM reflash is either done to improve the performance or make it more to your liking or to match an aftermarket ECM with its new vehicle.
Flashing because of Vehicle Issues — If your vehicle is showing false error codes, has a hot or cold starting issue, experiences idle roughness, stalling, or an emissions failure, it may be because the existing software needs to be replaced.
E C M (flash game)
Without reflashing, the data stream from an aftermarket computer that the other components in the car rely on will be missing or not meant for your specific vehicle.
Essentially, the ECM adapts cars to their drivers, in order to ensure those drivers are getting the most out of them in the most efficient way.
Description: What makes engine computers especially advanced is the fact that, not only are they tailored to your specific vehicle, they are also able to learn about you, your driving habits, and the conditions you typically drive in. This is where remapping an ECM comes in.