1. A system configured to measure affective response to content in a manner that conserves power, comprising: a content delivery module configured to expose a user to segments of content; wherein the segments comprise first, second, and third segments, and the user is exposed to the first segment before the second segment, and to the second segment before the third segment; and a controller configured to select a mode of operation for a sensor used to measure affective response of the user; wherein the modes of operation comprise first and second modes of operation; and wherein power consumption of the sensor when operating in the first mode of operation is at least 50% higher than the power consumption of the sensor when operating in the second mode of operation; the controller is further configured to: receive tags indicating when to operate the sensor in the first mode of operation, and to select a mode of operation for the sensor based on the tags; wherein responsive to receiving first and second tags, indicating to operate the sensor in the first mode of operation when the first and third segments are presented, the controller selects: the first mode of operation for the sensor to measure affective response while the user is exposed to the first segment, the second mode of operation for the sensor to measure affective response while the user is exposed to the second segment, and the first mode of operation for the sensor to measure affective response while the user is exposed to the third segment.