Now let's look at what instrumentation is. Instrumentation is one of the ways through which you can add diagnostic features to applications. It can be formally defined as follows:
''Most applications will include diagnostic features that generate custom monitoring and debugging information, especially when an error occurs. This is referred to as instrumentation and is usually implemented by adding event and error handling code to the application."
-MSDN
Under normal conditions, data from informational events may not be required, thus reducing the cost of storage and the transactions required to collect it. However, when there is an issue with the application, you have to update the application configuration so that the diagnostic and instrumentation systems can collect informational event data as well as error and warning messages to assist in isolating and fixing faults. It may be necessary to run the application in this extended reporting mode for some time if the problem appears only intermittently.