Metricsfordesigners@calexity provides a summary of why designers should care about metrics and how to track key metrics to prove the impact of design work. The document recommends tracking acquisition metrics like number of new sign-ups, activation metrics like number of people who click to book, retention metrics like number of return bookings, revenue metrics like total booking revenue, and referral metrics like number of sign-ups from referral links. It stresses the importance of questioning the data by considering both technical and human factors that could be influencing metrics.