From PsychoWiki

PsychoStats » PsychoStats Configuration » Error Logs

The error logs show all information, warning and fatal errors that PsychoStats has encountered while processing stats. Admins can view the logs for troubleshooting purposes.

One example is when a clan is not being detected in the stats and you can't determine why. If you enable the '-debug' option when you run stats.pl it will log information as to why each clan was not allowed to rank in the stats.