Good question.
On some cars the ecu can adapt enough to advance ignition timing and add more fuel like a remap would for your engine mods, but on some the ecu is so well developed it doesnt leave much room for mods.
In essence it makes the car perform better if something has changed.
However a live remap will yeild much better results as the ecu reset can only do so much where as moving the barriers further (what a remap would do) is obviously better...