In essence, you could exile a bunch of instants or sorceries from your hand to tee up a big flurry aimed at your opponent, while also getting access to more card draw with which to punish them
Many game stores are known to buy boxed bulk for a certain amount per 1,000 cards, and you could even try to sell a huge collection of commons as a lot on somewhere like Facebook Marketplace
It also works alongside Urza, Lord High Artificer and other cards that want loads of cheap artifacts
Customized treatment designed for your needs
You can choose from the likes of a Winnie the Pooh honey wizard, a stone gargoyle Beast, or a battle-ready Mulan, among many others
Given that nearly all of the value in MTG lies in rares and mythic rares, it means that Double Masters packs are technically worth more than normal, which is nice - but that worth should be for the players alone and not for Wizards of the Coast