Listening effort is a commonly reported difficulty among those who have hearing loss. A person’s ability to engage or disengage mental resources at strategic times could be an important signature of a person’s capacity to guard against wasted effort. This experiment gave listeners an opportunity to voluntarily reduce effort at specific moments based on the expected value of the incoming signal. First, sentences presented in the clear were immediately repeated, inviting reduced attention to the first presentation. In a second condition, the immediate repetition was randomly dropped on some trials, inviting increased vigilance to the first presentation. In a third condition, the first sentence was presented with degraded quality, inviting increased attention to the repetition to disambiguate misperceived words. Pupillometry was used as an index of moment-to-moment changes in listening effort. Data showed elevated pupil dilations linked in time with the disambiguated words and diminished pupil size specifically when there was less value in attending to the signal. These results support the need to expand the concept of listening effort beyond a “more” or “less” framework, toward a framework of efficiency.