If an object has one or more children or other descendants, you would expect that when you apply a modifier to that object, it would apply to the descendants as well. At least for the Array and Mirror modifiers, this would be extremely useful.
However, this does not happen. Empty objects are recommended for grouping objects together, but they cannot even have modifiers -- there would be no point, unless they could be applied to the children, but this doesn't work even for normal parent objects.
I tried to report this deficiency as a bug, but it was immediately closed as "Invalid", by somebody who apparently didn't bother to read it.
That bug report has some examples attached, of a situation where this ability is in fact rather necessary -- empty parents are being used to apply coordinate transforms, rather than grouping objects, but this then prevents the Array modifier from being used in the necessary way.
Is there any rational reason why at least the Array and Mirror modifiers cannot be applied to child objects, at least as an option?
Other people are asking the same question:
It's been suggested that my question is a duplicate of the one above. They are certainly related to the same issue (which is why I included the reference in the first place). However, the question that person actually asks is "What am I thinking wrong?" -- as if he's misunderstood the situation. I don't think I have misunderstood the situation, and the question I'm asking is why at least the Array and Mirror modifiers don't work in the way a lot of people would expect.