This sounds a little weird but what it does is necessary to keep your database up to speed.  The Pack is built into the Utilities / Backup-Restore / Backup option and needs to be done everyday the database is used.

The Pack All will:-

• Remove any records marked for deletion (entries in red) in the Thesaurus, Data entry, Circulation
• Tidy up any un-necessary blank space in your database

Alternatively you can choose to Pack only certain modules ie Circulation, Thesaurus and Catalogues