Elsewhere, during a discussion of House Rules, this thread was referenced: Old thread asking about the spell - Influence
After skimming the thread, it got off track about helping curb the Inluence spell, which could easily be curbed by not having the spell work until it became permanent. But then people will naturally point to the mechanics for making a spell permanent where the effect happens immediately, which is how Influence (to me) gets abused.
I thought of the standard example of using Influence to have a guard decide they need to use the bathroom, they leave their post, the runners move past the post, all in far less than 15 turns required to make the spell permanent, so the magician no longer needs to sustain the spell and it never bacame permanent. In my mind, then the spell should not have provided the benefit, but I don't feel like arguing about it.
Since then, I thought of a better example, or even series of examples. The magician casts Influence through the ballistic glass of the guard shack: Buzz the door open. The guard buzzes the door open, the runner team starts through the open door on the next turn. The magician drops the spell because why sustain it 14 more turns? The magician sees the guard going for the panic button and casts Influence: It is useless to hit the panic button; it hasn't worked for weeks (or some other suggestion forestalling hitting said panic button.) The magician only sustains it long enough for the other runners to engage the guard. The magician drops the sustainment after a turn or two and casts Influence on the guard: resistance is futile; I should surrender before they kill me. The guard surrenders and is restrained, so for a third time the magician quits sustaining the spell. This entire scenario could easily play out in much less than 15 combat turns.
All this is perfectly legit by the rules, but it breaks the need to have the spell be permanent which is a rule for using the spell at all. The really exploitive player will design a Sustained version of the spell, meaning the spell only works as long as it is sustained, and get a Drain reduction to further exploit the rules.