Your money remains in a vault unit you come to pick it up later.
Banks are not storage spaces. They are business. Thus they must profit by providing a goods or service. One of the goods and services a bank can provide is fronting the money that one may not have at a certain time, so they may purchase say, a house, and then make incremental payments as been agreed upon. You may sometimes call these "bills". When you deposit money, some of the profit will accumulate as interest and be awarded to you, according to the degree of money your deposit and the time deposited. Hence the incentive to use a bank.