You can use event handlers for many things, but a few ideas are:
• Monitor and log activity. For example, you can log actions to a log file, and later use that information to analyse what parts of a project have been edited.
• Synchronize another program or file with actions inside Source Insight.
• Alter the way that Source Insight works.
• Perform post-processing of files before saving them.
• Perform pre-processing of new files.