My current employer has just completed an Observability Week trying to raise the quality of how we understand our system.
Properly implemented Observability allows you to see the impact of your changes. Its great when you can see a cliff in a graph going hopefully in the right direction.
Observability allows you to answer the question how do I know that the change has worked and by how much. In some cases you want one graph to change and another to remain the same. Its not always possible to show a direct impact but for bug fixes or work driven by log analysis this is important.
Developer Rants 