Marcelo insists to his students that the Ankle Pick from Butterfly is a beautiful tool against an opponent in two situations: 1) at the start of a match when the opponent is kneeling with his foot posted (aka "Combat Base"), and 2) immediately on the rebound after recovering your guard from an attack. Also, Marcelo coaches his students to finish what they start; if you fight for the sweep, whether an Ankle Pick or even a Double, you cannot stop until you can establish a stable control. Double Under Control vs Butterfly is not enough -- in this position, you have to continue fighting for better control, otherwise you run the risk of the opponent framing and having to start all over again.