Why does creating a new account and making it an administrator require system restart? Why does creating a new account and making it an administrator require system restart in macOS?

I do the following:


login to macOS (El Capitan) as admin1
open Users &amp; Groups Preferences
add a new user admin2 using + button
check Allow user to administer this computer


OS responds with:


  You must restart the computer for your changes to admin2’s administrator settings to take effect.


The question is: why?

If I restart OS and login again as admin1 what has changed compared to the state before restart? admin2 was a just-created user and there were no processes nor other active settings that depended on it.
This only applies when changing the administrator status of an account after creation. When creating a new account as an administrator, the message is not shown. The OS doesn't keep track of whether or not the account has been logged in before, so changing the account type of an existing account asks you to restart in order for it to take effect.