Which, as the names imply, also effect fuel use and efficiency, the slower accelerating options are slightly better on fuel use. Think of it as you accelerating by gently pressing your foot down only a little until you are up to speed as opposed to pressing the pedal to the floor to speed up quicker.It's basically how the car accelerates when trying to achieve the set ACC Speed
I left mine in Eco to see if it was suitable when I first got my T-Cross and basically forgot to change it to any of the others. I find the slower accel to be fine and if I'm in much of a rush I can always press the accelerator. As for overtaking I just tap the accelerator when I'm over taking and then lift my foot again to let the ACC take over when I'm past.I find Eco and Comfort too slow if pulling out to pas slower moving traffic on the motorway.