A savings account isn't cash, its an immediately-callable loan from the account holder to a financial institution; for the account holder, it provides an asset with very good liquidity (but perhaps marginally worse than that provided by a checking account), essentially zero risk, but poor returns (but perhaps marginally better than that provided by a checking account). Its a way of meeting short-term spending needs (but perhaps slightly longer term than that met by a checking account).
Demand deposit accounts (both checking and savings) in general are, like cash, basically for short-term spending, but where the bank provides some benefits (actual storage, along with access mechanisms more convenient for many uses than pulling physical bills out of a storage locker).