It's that "whatever" that'll get ya. Does that footswitch take you one preset higher or one preset lower? Or does it call up a specific preset? Or have you programmed it to do something different in the current preset? If the mini-display just tells you where you are, then it gives you no clue as to what it'll actually do.
When I stomp on a footswitch, it's because I want to change something. And I want the mini-display to tell me exactly what that change will be. So I don't have to guess or remember. I already have the main display to tell me what preset I'm on, with 100% accuracy.
In other words, I don't want the mini-display to get lazy and just echo information that I already have available. Otherwise, why have it at all?