Credit booms have often led to credit busts and sometimes to painful economic downturns. When the bust comes, those who have overborrowed tend to sharply reduce their spending. Defaults typically rise faster than had been expected, which may put financial institutions into distress. These effects may combine to bring a serious economic downturn.
We have to see how the rules work in practice and what impact they 1/2  BIS central bankers' speeches  have. But still, we can reinforce the framework without introducing new rules or reworking its architecture. The next step is now to faithfully implement Basel III around the world.