Interest rates are called the price of money; or, the rent you have to pay for renting money.
The important effect of this is that when you can take a high rent for your capital, this motivates you to postpone consumption, save, and rent out the saved capital.
Negative interest rates motivate you to do the opposite: Consume what you have and then some, go into debt, and get payed for it.
So credit shifts consumption into the now; from the future.
The attempts of the Central Banks to enforce NIRP (and ban cash to be able to enforce it) have to be judged with this in mind: It is ONLY necessary to forestall the inevitable debt default of the USA and some other high octane money burning regimes like say Greece or Italy. The reason these regimes spend like drunken sailors is of course vote buying via the welfare state. Those who call this as failure of capitalism ignore that the welfare state is not a capitalist entity, rather the opposite.
Well anyway. I wanted to preserve this important notion that interest rates shift consumption along the time axis. This will become important in all future economic modeling.
And I got motivated to write this post by the weapons grade lunatic Ken Rogoff who is on the warpath against cash.