Becoming a bank holding company means that it can be transformed into a commercial bank, which can not only absorb deposits and issue loans, but also continue to do what securities companies can do before.
The significance is that this can help Goldman Sachs and Morgan Stanley transform into banking financial institutions with stronger capital, that is, they can change the current tense financial situation by absorbing deposits, and they can also borrow from the Federal Reserve without guarantee to deal with the financial crisis like banks.
It must have something to do with it, because the financial crisis has evolved to the present, and independent investment banks (securities companies) have been unable to survive, announcing the end of the era of independent investment banks.