Basically none in practice, but there are some hybrid collector-players who like the idea of building decks from their collection as opposed from all decks, and bristle at the idea of someone else not doing that. (And of course the collectors and WoTC themselves like to push for it because it makes them money: WoTC officially pretends that the secondary market doesn't exist but their actions make no sense if they aren't crafting their ~~loot boxes~~ booster sets with the idea of rare and valuable cards driving a lot of the demand).

(I personally think that if you want to force everyone to pay for product, play sealed or draft. Then everyone's on an even playing field budget wise, and it's more interesting than just net-decking. I'm sympathetic to the fact that WoTC needs to make money, I'm not sympathetic to their approach of chasing whales and making large chunks of the game basically inaccessible by their definition of 'legitimate play')