Whom should you include on your contact list? why?

To be honest this question is actually a lot more broad then it seems, because it depends on the persons age, relation, and social status that displays who they might have on their contact list. Like for the younger audience it might be a good idea that they have their parents phone numbers on them. For a more teen toward audience most will Skype or use other social to connect with, so maybe not as much contacts or little at all, even parents may not be included in it. For the adults it would be more for contacts of colleagues, wife, your kids, etc but friends may be a factor in that as well.