'Sport' mode is for more aggressive driving, where you might need rapid acceleration. For cruising along a motorway, you can simply go for the bet fuel economy, which means selecting 'Eco' mode.
No one needs an eco setting. If you want economy just get some willpower and drive economically.
What's more it might reduce the power available to you. When you have misjudged the tractor overtake, you won't have the oomph to get you out of trouble.
//No one needs an eco setting. If you want economy just get some willpower and drive economically.//
That is not necessarily true. Auto's will stick in the gear for longer (higher revs). For instance mine doesnt go into 8th gear at slower speeds on a Motorway.
As stated above, Sport is to get better acceleration, not required on a motorway. Of course you can always go into launch mode to get away from the lights real quick although my manual suggests not doing it too often dues to the stress on the drive train!