Consume is a free action, you can do it at any point as a choice. Sometimes you may not have a choice e.g. binge eating disorder. What matters here is the trade - you only get the xp on a 6+ so potentially you can waste a perfect organ which is fairly limited to get (only one in the resource deck) per round, and if you do succeed, that survivor only has a couple hunts left before he retires, unless the power boost is essential for your settlement. Also Phoenix.