'Signing out' from your account on a PS4 brings you to a menu with a list of accounts you can switch to - meaning the only action you can take from there is sign into another account. However, signing out also turns off the PS4 controller.
If you were going to turn off the console, there's that option in the menu to begin with, and it signs out automatically anyways when turning off the system.
So what purpose is there for a Ps4 controller to turn off when signing out?