Maybe it can be useful, but logic tells that only security should receive it (not police).
And sec`s duty is to stay close to presi all the time. So... Probably not that useful.
For the first part, there are some cops that REALLY wanna protect president (including those who couldn't pick security class and those who like cops for uzi) , so the backup msg should reach all the protecting class members. It won't harm anyone anyway unless the announcement is right where the players get the crosshair on screen.
There are some securities (mostly regular players) that try going away from presi's camp place to get a refill when they 'think' is safe for a while. And also , some securities try getting a heli/boat/bike etc for the president , leaving him with other secs. So a backup msg might be helpful to alert such securities that presi is under attack. oh, and i forgot to add the nrg whore presidents. He might need it when his nrg fucks up.