As far as the total economy goes, doesn’t any money not spent on gasoline get spent somewhere else. Most live paycheck to paycheck, so if it isn’t going in the tank, it is going to clothes or a house or a hairdo. If money is saved then that hurts the economy doesn’t it in the short run?
If you spend more than you need to, you’re wasting your own labor. It may help someone else but it’s not mutually beneficial. See the broken window parable. https://en.m.wikipedia.org/wiki/Parable_of_the_broken_window Also, money saved can be invested to produce more wealth rather than simply consuming it.