You can delete all of the entries in a terminology database without
removing the database itself. This saves you the trouble, if you want
to clear out the terminology database due to a faulty import, of creating
a new TD into which to re-import the data.
Purging a TD retains existing TD group memberships, AIS assignments,
and any other references to that TD in WorldServer. Therefore, purging
a TD saves you the trouble of recreating those TD references as you
would when deleting a TD and creating a new one from scratch.