You mean that if I execute the ALTER DEFAULT command above as user `postgres` then only tables created by user `postgres` will give default privileges to role `webapp`?
Yes. "You can change default privileges only for objects that will be created by yourself or by roles that you are a member of."
You use the "FOR <target_role>" modifier if you want the "or by roles that you are a member of" portion to be used.
David J.
