postgresql documentation says:
All timezone-aware dates and times are stored internally in UTC. They are
converted to local time in the zone specified by the timezone configuration
parameter before being displayed to the client.
timezone parameter is a session
parameter<http://www.postgresql.org/docs/9.1/static/runtime-config-client.html#GUC-TIMEZONE>.
When all TIMESTAMP WITH TIME ZONEs will be stored as UTC and the client
connection will specify the session timezone, then what is the benefit of
setting TimeZone parameter in postgresql.conf?