The Eco light on the dash simply means your throttle input is very low there is very low load on the the engine so you are optimizing fuel efficiency. On some toyota engines, it indicates a pseudo-atkinson cycle mode with modified valve timing that further optimizes efficiency. This is all in the background and not controllable by the driver except by being very easy on the throttle. I don't think the 3UR has this atkinson cycle type of design.
On the LX switching to ECO in the drive modes dulls throttle response and seems to give lazier shift points but doesn't actually change power output otherwise. I'm not sure if there is an ECO switch in the LC. One useful option I did find after moving from the 40 and 120 series forums to the 200 series is the "ignore" button since there seems to be a lot more passive-aggressive and not-so-passive-aggressive participants here than other places on mud.