I honestly don't use it that much. I guess it could be used sort of in the same way that feign death is used, but mainly in PvE. I know it reduces some threat.
One way you used to use it though was to set traps. When traps could only be set out of combat, you would set one, attack, keep pet on passive, disengage, set trap, attack.
I believe that used to work, but now it is kind of obsolete because of in combat trap setting.
Maybe someone else might have a better example