Their system automatically makes a winner of the biggest party. In any country that uses that system, it automatically leads to two main parties alternating in power. The advantage is that you don’t need “messy” and “unstable” coalitions, but can have strong leadership with a solid base instead. Except that perhaps string leadership is a dangerous thing to have in many cases, and except that if the balance tends towards 50/50, you can easily have problems getting anything done.