https://www.investopedia.com/articles/i ... -money.asp
https://www.investopedia.com/terms/q/qu ... easing.asp
The government is essentially acting as the central bank and controlling money supply via the deposit sweeping mechanism
In the real world, central banks will expand money supply (cut interest rates) or conduct quantitative easing (buy bonds) to boost GDP. Cutting rates and buying bonds will lower interest rates in the market and expand the supply of money available to be lent out which will boost GDP.
Since we don't have a mechanism that enables the government to influence money supply, the fund sweeping mechanism will do just that - today, if the gov. runs a large surplus, (through higher taxes and what not), it is depressing consumer GDP and hence, the demand for goods and services and vice versa. Hence, this new feature will do four things to the game:
1) Allow government action to "influence money supply" and hence, economic activity.
2) Enhance competition in the banking industry by "rewarding loser" to allow them to fight for another day
3) Reward/punish governments for their fiscal choices
4) Allow government to earn a return on its surplus capital
I think this is a much better way of emulating monetary policy rather than allowing the player to mess around with interest rates - Since under the scenario where there is no inflation, if you allow players to choose, they will always pick an interest rate that is most favorable to their firm, which will make the game quite unbalanced.