If you let them use Aether Vial to generate mana, they can start producing things that get in the way faster than you can answer them
Yoshimaru, Ever Faithful One of my favorite white commanders, Yoshimaru, Ever Faithful can be surprisingly powerful when built correctly, especially in Duel Commander
One positive is that self-mill effects tend to be much cheaper than actual card draw, meaning you can access a larger chunk of your deck earlier in the game
Bane of Progress is particularly good with Ygra, as the former will get a +1/+1 counter for each artifact and enchantment destroyed and the latter will get two +1/+1 counters for each artifact that hits the graveyard
The cheaper and better ones like this do so the most and it makes the biggest difference to singleton formats where redundancy is such a tough thing to attain
Many competitive players maintain both English for tournaments, Japanese for their personal collection