Chapter 12. Baselines
The last change is the first blamed.
Baselines are a key concept in maturing the use of performance information. With a baseline report you effectively take away the private view of the data presented in the APM workstation and share it among all of the application stakeholders. This is critical because access to the APM workstations is often limited both from a "needs some training" to a "we bought it, only we use it" perspective.
You also directly address the first question that arises during a performance incident: "What changed?" You achieve this by presenting evidence that suggests that the application, or one of its resources, is operating normally. This allows the triage effort to then focus on other areas. Conversely, ...