IDM_OBJECT_STORE table contains information about configuration changes in OAM 11g. It gets updated with latest file whenever there is a change in configuration. This table keeps older version of changes as a backup.
In case of Development environment this table may be huge. In case space crunch we can purge the data from this table as well. There is OOTB utility present in OAM Binaries.
purge_config.sql script — <oracle_home>/common/sql/purge_config.sql.
Before purge make sure you have a backup in case of any issue.