Why is it necessary to grant access to PostgreSQL sequences? Using PostgreSQL I see that the pg_dump command (and probably other commands) requires access to 'sequences'. I understand these to just be incremental IDs that are necessary for row identification...
Why is it necessary for server roles to be granted access to sequence objects? What are the potential security problems if every role had access to all sequences of accessible schemas?
pg_dump needs to dump the current position of the sequence, so that it can be restored. Otherwise, the restored sequence would start at 1 (or whatever its start value is) again and would generate duplicate keys.
Granting SELECT on the sequence should be enough for that purpose. Then the user can see the current value, but cannot increase or reset the sequence.