What I meant (but didn't say very well) was in the mad scramble to not be the second highest vote getter, voting for Terry or Sally will (probably) be forgotten. Self preservation should take the target off T & S all together.
In a way, it's similar to The Cindy boot. Soon as Cindy knew Rafe was targeting her, she targeted him and booting Danni went from almost a sure thing to not even being considered.
I think that's where the power of holding the idol lays.