I have looked for a relevant answer to this question and not found it, so am asking the question myself.
I am asking this question because my most important motive for setting up a Tor exit relay is to help people in countries where censorship and surveillance mean that it is really difficult or dangerous for them to use the internet to discuss historical, political and religious issues, however non-violent their approach or activity.
One key background experience which explains my view of this issue is that in the 1960's I lived in a country where it was illegal for bookshops to import and sell "Nineteen Eighty-Four" in English by George Orwell, or any other book written by him. It was not illegal to own a copy, or read it. This was in Europe, but not in central, southern or eastern Europe, in case anyone is wondering. Of course this did make me pay attention to the novel when I was lent a copy of "Nineteen Eighty-Four".
Is there any effective way that I can specify the countries where internet users can use my relay? I would not be aiming to stop internet traffic passing through any countries, just ensuring that the users of my relay are in some countries that in my judgement have a greater need to use Tor more, rather than others that I would judge need it less.
Or does the way Tor works as a system overall mean that any narrowing of the range of countries where users will use my relay will be automatically compensated for by the Tor system, so any change of this sort to my relay can have no overall effect on users, even if many other users made the same changes as those I am asking about?
So do I just have to accept that helping some people to watch cat videos in a secure, private and anonymous fashion, or others to do something I would regard as rightly illegal as well as morally wrong, as the inescapable dead-weight cost of helping others to achieve the ability to discuss and learn about important issues as free adults?
I can accept that there might be nothing more that I can usefully do to increase the objectives that led my to run a Tor relay, but I definitely would like to know whether that is true or not.
It would be useful to know the answer when other people question or challenge me about my Tor relay helping criminals to hide their nefarious activities.