The saying 'cash is king' is a popular financial expression because it emphasizes the importance of having cash on hand. Cash provides liquidity and flexibility, allowing individuals and businesses to quickly respond to financial needs and opportunities. In times of economic uncertainty or market volatility, having cash reserves can provide a sense of security and stability. Additionally, cash can be used to take advantage of investment opportunities, negotiate better deals, or cover unexpected expenses. Overall, the saying 'cash is king' highlights the value and power of having readily available funds.