The reason to save is so that you don't need to borrow in the future. Not all savings are immediately lent out, and it's only because of inflation that anyone feels like they have to, because savings not invested somehow will be diminished by inflation. Inflation forces people to lend and rewards borrowers, encouraging a society of people constantly scrambling to service their debts, terrified of all their "savings" (that aren't actually set aside, but are being used riskily by others) vanishing with a fluctuation of the market, and a tiny fraction of people with absurdly huge and diversified assets (the big lenders and rentiers) reaping the benefits of all that debt-servicing by other people.
Of course deflation has its own problems too, causing those who have more to get more, more quickly, without having to do anything for anyone.
What we really want is a stable currency, with no inflation or deflation, where people can work, actually save when times are good instead of "investing" their earnings in risky ventures, and then "borrow" from themselves (spend from their own savings) in the future when times are lean.