Our economy is based on the circulation of money. That's why the money you put in a bank is not just sitting there, it's being loaned out and circulating, and you hope the bank has enough funds to cover it when you want to make a withdrawal. When people spend money, they're helping it move around.
Classic example, a man visits a hotel on vacation and accidentally leaves a $100 bill on the dresser when he goes sightseeing. The maid steals it and gives it to the butcher to pay her outstanding bill. The butcher gives it to the cobbler for fixing his shoes. The cobbler gives it to his mistress as a gift. The mistress gives it to her sister, the maid at the hotel, to pay her bill at the butcher shop, not knowing that she already paid it. The maid puts the $100 bill back on the dresser, thankful that she won't get in trouble for stealing it. No one saved any money, everyone had a reason to spend money, and the total amount of money in the local economy didn't change, but the economy received a boost, none-the-less.
Individually, people are better off saving their money. Collectively, we are all better off when people spend their money.