When the oil level in your cars engine oil pan is overfilled and too high then you risk blowing engine seals and causing severe engine damage since the oil cannot move around in the oil pan and throughout your engine like it should.
The oil is constantly being pumped from your engine oil pan and distributed throughout your engine where it then returns back to the engine oil pan to repeat the process over and over again.
If the oil pan is overfilled then the oil cannot circulate and return to the oil pan like it should and you can blow out seals and other things in the engine.
If you overfill the engine oil by just a little then it's likely okay but if you add a Quart too much of engine oil then you need to drain that amount of oil back out until the engine oil level is correct.