There are several "family" apps available for mobile devices that allow you to share things about your family: shopping lists, calendars, occasional device locations, that kind of thing. At least two of these applications (and if there are at least two, I am concerned that they are all) use the very interesting The practice of requiring users to be part of the same "family" group uses the same password (however, different user names).
The justification given by at least one of these applications is that the password is used to determine which group the user belongs to, but I am a programmer and I am pretty sure that the explanation went through the back of a male cow. However, what I am not is a security expert, and although I'm pretty sure that enforcing shared passwords is a bad idea, I can not express it. why Is it a bad idea.