For the record, this is what the 170 Supplement says:
Eco mode offers increased fuel efficiency and quieter exhaust character, as well as a more relaxed throttle pedal recommended for wet weather conditions.
• Eco (if selected, will stay active on subsequent igni-
tion cycles): Offers quieter exhaust character, maxi-
mized fuel efficiency, and increased throttle pedal
control for wet weather. Shift paddles are disabled.
Steering and suspension settings are configurable.
I haven't noticed a change to the pedal or exhaust based on a few dozen miles driving around town, but the difference in the trans it huge! I'm guessing the bulk of the "eco" is earlier upshits on mild throttle and the less aggressive downshifting.
I plan to keep it in eco unless I plan to play a bit.
