There is two ways of tunning your car.
1. One is to make your car easier to handle, easier to drive for you so you don't have to fight with your car. This does not necessary get along with the speed, but you can take corners easier and always had a good smooth line. Good smooth laps. This way you can feel your car and always have the control over any tuned car. This is the method to tame any car you want.
2. Second way is to make your car faster, kind of harder to handle in corners. You loosing down-force that helps you in corners, you have to brake a little earlier and every corner must be mastered with the racing line your car can handle. In this way you find yourself fighting with tuned car and always unsure if you manage to finish lap or entire race without going off the track. So in this method you must adapt to your car, not the other way around.
In both ways it's a learning process of how far you can go with the tool you have. We all want to drive fast and make our laps better so every time you tune your car you must choose if you want to have total control and very easy work on race track of maybe you want to fight a little harder to gain some time.