It's currently impossible to add a visibility parameter to a group instance.
To have a Visibility parameter available for groups would greatly simplify the creation of families.
One example where this is necessary is when you're creating an array in a family. Arrays need a minimum of 2 elements to work.
But in cases when an array only needs 1 element, we should be able to set the second element to invisible.
Something in the likes of "Array < 2" uncheck the visibility of that last element.
But I'm sure there are other examples, when creating families, where this function is desirable.