It sounds simple but it's not. Take android for example, i thought i could quickly set up a guest/party account without my email and things like that. Creating the account and selecting the allowed apps was very easy, the problems came later.
First, all my system settings wasn't cloned, to the new account i had to re-add things you take for granted like my localized keyboards and stuff like that, can't remember if wifi passwords were included or not. Then comes application settings, many apps are unusable before you configure them properly, even the web browser is unusable in the default state on high dpi devices, you must change the default zoom level. Then it seems some apps actually share state, and in some cases rightfully so, finding out how they share it is a mystery. Some are designed with multi user in mind so you can in fact have a mail app accessible on both accounts without sharing your mails as the system accounts are linked to different mail accounts. Others are the other way around, maybe you want your 10GB music collection to be accessible from every account? Drawing the line of where and what should be shared is very difficult.
