Why? The Benefits
Diagnostics falls into the middle ground between Quality Assurance and Operations Performance Validation.
For developers, having Diagnostics means that tracing code doesn’t have to be added and removed. This is a big side effect of why diagnostics can improve performance.
Diagnostics is the science of pinpointing the root cause of a problem. Load Runner is the first load testing tool to provide a set of Diagnostics modules that trace, time, and troubleshoot end-user transactions acrossALL tiers of the system. These modules extend LoadRunner to provide a unified view of both end-user experience and application component (method, SQL) level performance. The intuitive visual interface allows the user to drill down from a problematic business process all the way to the poorly performing component. This granularity of results ensures that every load test provides development with actionable results, thus reducing the cost and time required to optimize J2EE/.NET applications.
Diagnostics can be integrated with HP Business Availability Center software, HP LoadRunner, and HP Performance Center
As the response times alone will not suffice the report, more people(client ,developer etc) are interested to know the key features why the bottlenecks .As a part of performance engineering identifying the root cause as where the bottleneck is and why is it caused.