If two people ban the same champion one of them should get a another ban...
If two players on opposite teams ban the same champion then one of them should have a chance to re-ban another. The player that locked in the ban second should have a chance to re-ban another champion. So that a ban is not wasted. It is much more efficient.
For example:
1 person from blue team banned Yasuo 1 person from red team banned Yasuo
The blue team locked in the ban first thus the player on red team gets to ban again.