Identify popular Request Types, Incidents or Faulty Products using an aggregated view of tickets by custom fields.
Pick the custom fields to report on, leaving out the rest. Keep your reports focussed on solving key problems first.
Identify which custom field values are least used; Which custom fields are not being filled and improve support processes.
View custom field value data by time. For instance, identify which error type is gaining popularity and preemptively fix them.
Dissect your ticket data by contact custom fields, to identify which class of customers create most tickets.