Earlier quoted context omitted.
You raise fair points about the spending of money on physical assets/consumption. Can you elaborate similarly on the potential problems with how saved/invested money is allocated?
Well, at a very high level, banks can use saved money to lend to businesses or individuals at a given multiplier. If a bank has insufficient deposits, it can't lend any more money. This is called fractional-reserve banking. https://en.wikipedia.org/wiki/Fractional-reserve_banking So when you make a deposit, you are effectively causing a fraction of that deposit to be available for lending. This is what you're getting…
That's not actually true, banks effectively create money when making a loan, and the only constraints on this are the interest rate set by the central bank, which affects both demand for credit and the cost of providing it, and liquidity requirements set by legislation.
https://www.bankofengland.co.uk/-/media/boe/files/quarterly-...