Modifiers on the Empty
Modifiers on the Empty (Empy) that propagate to child objects when possible. They modify the entire group, not the individual objects. Imagine you have a complex object with various meshes parented to an Empty (empy). You want to duplicate/multiply it entirely using an Array.
2 Comments
Collection modifiers might be a better solution, more flexible and future proof. Empties should be as simple as possible.
Putting a deform on an empty or other parent object, which ripples down to the children, can be incredibly useful and flexible.
Collections cannot be moved and rotated as a parent, so having them be the owner of a deform, which translates into members would be a very odd thing to work with.