It allowed them to create more money. Fractional reserve requirement is something like 1/20, no? But usually the capital (bank company equity) requirements (like Basel III) were the harder to meet, so who knows how much new money banks created. (Actually it can be easily looked up, and not much, because inflation did not jump.)

Usually QE allowed banks to roll over mark-to-market assets that turned into garbage into sane cash to satisfy solvency and liquidity requirements. And of course this led to price stability.