It depends on the age/mileage of a car and a variety of factors. Some engines respond better to remapping than others. Some are sold at a low state of tune from the factory, yet others have already been pushed near to the maximum power other components (such as the gearbox) can safely handle. Reputable tuning companies will only tune a car to a level it can take, but it wouldn't be a good idea to remap a car with a sketchy maintenance history or very high mileage. We'd speak to tuning outfits such as Quantum Tuning, Superchips or Celtic Tuning to see if your car is suitable.