Valve springs are good security. Things like seat pressure and coil bind come to mind. A standard valve spring will move around on its retainer causing harmful harmonics and excessive wear. Your car will still make power but your springs are being forced onto their retainer is very likely to fail at the coil. You will soon enough loose seat pressure and power will diminish and the standard spring will get weaker and weaker until it fails, and when it does fail you will certainly know about. Sometime you have to do modification the help you make the power. You'll be surprised how much smoother your motor will be and how willing and easier to rev. It's important to have valve spring seat pressure especially on a turbo car to insure tight contact between the valve face and the valve seat. This provides proper heat transfer from the valve to the cylinder head. Remember if the valve bounces, cylinder pressure and power is lost. If it happens over and over in time the head of the valve will deform & break from the valve stem resulting in engine failure. If you modify a car do it properly, but at the end of the day its your car and its really easy to make lots of power, but have you made it safely??