On the other hand, a minute may be enough to get the VIP out of the building or whatever place he's in, so that it's hard to know from the outside, where exactly to strike.
The TFR buys you that minute, because you know that something's wrong. If it wasn't there, your time window would be zero.
Of course, TFR violations seem to happen too often to really always evacuate the VIP whenever someone enters without authorization.