This recipe helps you when you are in doubt whether some obscure table is used any more or it is left over from old times and just takes up space.
Make sure that you are a superuser, or at least have full rights to the table in question.
To see whether a table is currently in active use (that is, whether anyone is using it while you are watching it), run the following query on the database you plan to inspect:
CREATE TEMPORARY TABLE tmp_stat_user_tables AS SELECT * FROM pg_stat_user_tables;
Then wait a little, and see what has changed:
SELECT * FROM pg_stat_user_tables n JOIN tmp_stat_user_tables t ON n.relid=t.relid AND (n.seq_scan,n.idx_scan,n.n_tup_ins,n.n_tup_upd,n.n_tup_del) ...