Why Bother with Product Metrics?

Good data helps you make better decisions.
You’re too close to your product to see things accurately. You need a clear way to see how people use things without relying on how you expect them to use things.
Metrics are also useful for important conversations. Hard data is one way to escape a your-opinion-vs-theirs discussion. 

Product metrics are the lingua franca of organisational change. 
Setting goals without a way to measure your progress is a fantastic waste of time. The only way to know if you’re moving in the right direction is with some kind of measurement.
The ideal metrics will vary from project to project, but a good rule of thumb is to focus on 3 to 5 key measures. 
My suggestion is to start by being able to answer the following 4 questions:
1. How many new people each month?

2. How many of them use our product for any length of time?

3. Of the people who stick with us, how much do they use us?

4. How much money are we making?
These four aspects (acquisition, retention, engagement and monetization) each capture a different,  but equally important, dimension of what’s happening with a product.