Metrics are important to investors because they provide visibility into a SaaS company's revenue growth, sales efficiency, and customer retention. Key metrics include monthly recurring revenue/annual recurring revenue to measure topline growth, revenue churn to understand customer retention, and customer acquisition cost and lifetime value to assess the efficiency and profitability of the growth strategy. Maintaining high growth, strong sales efficiency through a favorable magic number ratio above 1, and low revenue churn are positive signs for investors.