If you ever get into serious ecodriving you'll hardly ever see it
.
The idea is to have changed up
before the shift light comes on - if you wait until it illuminates, you've already missed the optimum change point for best economy.
But in fairness to the 99% of drivers who drive in, er, shall we say a more 'normal' way, IMO Fiat ought to make it possible to disable the shift light through the menu system. I don't think it's right for car makers to try to tell us how we should be driving. You earned the money, you paid for the fuel, so why should Nanny Fiat keep nagging you about how you're choosing to use it?
Those who find it useful could always leave it turned on.