_introspection : Instrumentation data about your Splunk instance and environment and writes that data to log files to aid in reporting on system resource utilization and troubleshooting problems with your Splunk Enterprise deployment .
- More details : About Splunk Enterprise platform instrumentation
About the licensing, it does not count against your license:
Use the "Indexing volume" status dashboard in the Search app to see details about index volume in your infrastructure. Note that the overview includes internal indexing, which does not count against your license.