The thing is if you push into enemy territory you are putting yourself in a disadvantage, whereas defending from a passive position puts you in the advantage. If you die during a rush and your teammates are unable to cover for you then that can also be game deciding.
But if you die during a rush your opponents have to move the tower farther than they would if you died defending the center. You have more time to respawn and intercept them.
These are both valid strategies but I just think constantly pushing the tower is safer most of the time.