The road bike I was enquiring about comes with a Shimano 105 CS580 11fach (11-28). I was on the phone asking what the difference is between the 11-28 and the 11-32. The guy explained that the 11-32 would be a better choice for mountainous roads. It never occurred to me to ask what the disadvantage is of using this sprocket when you are riding on flat roads. Anyone know? They also offered the 12-25 socket but I just assumed that was for even steeper hills?

The standard sprocket is stated as 11-28

The alternative options are 11-32 or 12-25