In 12.1, upgrade guide, the below is shown on page 1-14Please see Page 4-29 Step 2: Drop obsolete columns (recommended) for details – In the same upgrade doc for details.
During the upgrade process, the Oracle RDBMS DROP COLUMN command marks
Oracle E-Business Suite columns as unused in the data dictionary, making it possible
for the database administrator to drop the columns and reclaim the associated space. It
Planning for an Upgrade 1-15
is a good idea to plan this reclamation ahead of time because the process locks the
associated tables. Once the space is reclaimed, the upgraded data model looks more like
a fresh install (except for customizations). Note that DROP COLUMN has no effect on
How to plan for this reclamation ?. what is exactly being meant here ?