[Acolyte]

Well, the strong directive from both God and Lucifer, and prosecuted by all the Archangels and Demon Princes but especially Dominic and Asmodeus, is that the War should be kept as secret as possible.

Going about doing otherworldly things at random because it's "cool" is liable to get you all sorts of negative attention from your side and from the other side. Not to mention that spending Essence to boost rolls always causes disturbance, too, which is handing your GM the ability to make ANY passing celestial take interest. Finally, Essence is pretty hard to come by for most celestials (Impudites of Technology being the most obvious exceptions), and can get used up very quickly in a fight. You really, really, really don't want to get caught by the other side when your Essence is low.

So that's why this isn't abused.

That said, most Essence expenditure I've noticed in-game has been on Songs or resonances (Skills typically have higher TNs). Since a Song is going to do something pretty otherworldly already, Essence expenditure just kicks that up a notch (sickly green glows emanating from victims of a Song of Charm, a sizzle of electricity along the border of a Song of Shields, extra-special visual dazzle to go along with the boom of a Song of Thunder, etc).

Essence on a resonance roll, however, is a big change, since resonances are the one thing celestials get free use of with subtlety (barring high Roles). Using Essence to pump a resonance means 1) you create disturbance and risk catching someone unpleasant's attention, and 2) human witnesses will know something happened. I rule the visual effect as being focused on the resonance-user (unexplained light shines down on the Seraph's head while he questions you, an insubstantial whip appears in the hands of the Habbalite, etc), not the victim, making it especially clear.

But the really, really fun ones are when Essence gets spent on a Skill roll. That's when cars leave tracks of flame through the air, a chorus of damned voices wail out along with the guitar music, or when everyone's vision slows down to a picture-perfect slowmo while someone Dodges inescapable bullets. Good times.

All that said, though, these special effects don't overshadow the effect of the roll. If you Fast-Talk someone and pump it with Essence to get the guaranteed success, he'll let you break the rules as usual. Now, he'll spend the next five minutes convincing himself he didn't just see giant batwings spring from your back and your tongue fork like a snake, but odds are he's not going to trust you again in the future, remembering that feeling of foreboding.

Human beings are very, very good at overlooking really minor bizarre things, shaking their heads, and saying "that didn't just actually happen. Man, I need to skip that sixth cup of coffee." So don't penalize your players unduly for using this rule. But if they abuse it, don't hesitate to pull out the payback hammer.