It uses more fuel and runs the exhaust a bit hotter.
On an unrelated note the Jettas have also had problems with the high pressure fuel pumps and with condensing the post-cat EGR into water which pools in the bottom of the intercooler. Passats have an air to water intercooler, and don't have fuel pump problems
They get better MPGs too, even thought they're a bigger car (as big inside as a LWB W126!!!)
-J