Battlegrounds banning question

Why do people say you no longer have to ban someone once you have them? I see this frequently and don't understand the logic. Just saw a thread saying to rank 4 enchantress so you never have to fight her again. How does that make sense?
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Comments
Lol, once a player banned my onslaught and also my jack even tho my onslaught was 6r4 and his was 7r3 sig 200.
If u have the most meta options ( serpent, thanos, enchantress, photon, etc) at high ranks , then u might try to ban some creative options than just banning annoying defenders, like lets say ur opponent has a r3 shatra as the only serpent counter, and he might not ban ur serpent thinking he will draft shathra, but u end up banning shathra, tht is a really fun scenario.
It dos tell you in advance mode. Of it
We need hieroglyphics here.