Good question. Well, if I'm going to ask for the world - I would first want to identify anyone not related by blood or marriage, being those profiles that I've adopted while perhaps doing project work, the random profiles who've been adopted over 10 years. Those who are truly unrelated.
Then, I'd perhaps want the ability to identify anyone not related by blood, say the spouses of a relation of any degree.
Then, I'd perhaps want to identify anyone related by blood, but of less than x-degrees. Say, keep the great uncles, but not their children. Or, keeping the direct line, but not their siblings. Something flexible like that. Mainly I want to identify them, so that I can pick & choose who to keep, and who to orphan.