As might be clear this early, vouchers were developed as a way to avoid entrusting people being sent on an errand with real money. It is important to note that vouchers are issued for a specific task only- food, shopping, casino deposits, etc.
A company that wants to pay for its staff lunch will be wise to give them vouchers instead of money. With money, some will not eat for various reasons. Others may even spend the money on things that are against the company policy.
In which case, the company would end up scoring an embarrassing own goal. While some employees will still use underhand methods like selling their vouchers, the company does much control by issuing vouchers instead of cash. Further down, this article describes how this example is relevant to voucher use in online casinos.