In most cases, removing older rules decreases the overall upgrade time. Running the cleanup script permanently removes rules older than the current version from which you are upgrading. For example, if you are upgrading from PRPC 6.2 SP2 (06-02-20) to 7.3, cleanup removes rules of version 06-01-99 and older. Run the cleanup.bat or cleanup.sh script to generate an SQL script to clean up the rulebase. You can either have the cleanup.bat or cleanup.sh script automatically apply the SQL script, or have your database administrator make the changes.
Once the scripts get generated, pass in the appropriate version number to delete those corresponding ruleset. I hope you would not want to delete all the versions prior to 7.2.
For your application implementation layer specific ruleset skimming is recommended.