To earn money, somebody has to have created value (people are paid for creating value). Spending money is consuming value. Imagine there is $100 worth of total value in existence. Somebody creates $5 of value, they're paid $5, and total value existing is now $105. They could immediately consume or invest this $5 of value, leaving society with $100 of value, and if they invested some productively then they'd have increased the rate at which society's able to generate value in future. Or, they could do nothing with that $5, leaving society with $105 of value. How does society access this extra $5 of value? The person who choose to hoard the $5 effectively removes that money from circulation, which decreases the supply of money and hence increases its value. This means the purchasing power of other currency holders is increased. Those who then decide to spend money can consume or invest the $5 of value that was left unused.
