Adults could, of course, suppress their location by disabling Share My Location in Settings > iCloud, but then everyone in a group, including the other adult or adults, can't find them either. Let's not get coy about affairs and secret gambling habits and the like. It's a perfectly reasonable thing for an adult in a pair or other relationship to not want to be tracked by other people at all times, even when they trust them with their lives. And if your "family" is a group of people sharing a home and media, rather than a more conventionally structurally define one, it becomes even more of an itchy topic.
Without getting into games of logics and ethics, like the Prisoner's Dilemma or Two Hens and a Fox Cross the River, suffice it to say that the perfect panopticon of awareness of everyone's whereabouts in a group and the choice for someone to opt to be completely invisible aren't always the only desired options.
Wipe that smirk off your phone
The related issue is that Find My iPhone and Find My Mac become available to everyone in a family. Every device you possess and every device that anyone in your communal group has logged in to a participating iCloud account is part of this collection.
This is great when a device is lost or stolen. Rather than that person having to get to a browser or iOS device to log in and track their device, anyone else in the family can pull up the information. This is awfully handy while traveling together ("Ah, you left it in the hotel!"). If you disable location sharing, Find My iPhone continues to work for your account, and still provides limited access to the rest of your family group. Another family member can determine whether a device has an Internet connection, and can play a sound to help you or someone else find it.
Here's a potential downside: with location sharing enabled, every family member has the power to wipe every other device, iOS and Mac, that's part of the family group. Apple recognized that not all families are happy families, and that hardware might fall into the wrong hands. Thus, to erase a device belonging to another member of group, that member's Apple ID password is required.
So even in the hopefully unlikely event that one person has a device stolen or someone gains access to it and they have a password that can be guessed or is written down, that still only allows that malefactor to wipe the iOS and Mac devices belonging to that one account holder.
But this should alert you to the risk once again of writing down and sharing passwords. In a home with one or more shared computers, a sticky note on a monitor with the family's passwords — where it can be seen by family, guests, kids' friends, or even a burglar — becomes an even worse idea than it's been for decades.
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