Tracking metrics is important for understanding your business performance, identifying areas for improvement, benchmarking against competitors, and fundraising. The document defines metrics for nine common business models: enterprise software, SaaS, usage-based, subscription, transactional, marketplace, e-commerce, advertising, and hardware. It provides the definition and purpose of key metrics for each model and common mistakes to avoid, such as using bookings and revenue interchangeably or including non-recurring revenue in monthly recurring revenue calculations.