From Apis Networks Wiki

Uses

• Generate a tab-delimited listing of all files contributing towards disk quota
• Itemized breakdown of disk usage per user and per service (Urchin, Web logs, MySQL, PostgreSQL, and e-mail)

Notes

Disk reporting discrepancy

Reported disk space for individual users and services may not total the reported disk space in use. Files created by a PHP or Tomcat application from the Web server are not included in the reports due to efficiency reasons. These files are converted over to your quota through a batch process executed nightly.

Technical explanation: such a facility requires enumeration over all files within the filesystem attached to an account. Reports are generated in real-time and the cost of enumerating over the entire filesystem may cause significant delays in accessing the report.