The Importance of the Arms in Closed Guard
Anytime someone is talking about opening or closing an opponent's guard, they are speaking about the the opponent's legs and whether or not they are wrapped around the waist and locked at the ankles, or in one of the dozens of positions that fall under the umbrella of open guard.
When developing one's closed guard, the focus tends to be on placement of the legs around the opponent with the ankles locked. We can utilize a high guard with our legs wrapped around the upper back of the opponent and weighing heavy on their upper torso, or we can be wrapped around the waist area which would be considered a low closed guard.
In an attempt to break the posture of the person you have your guard you may reach for a lapel grip, or perhaps utilize grips that attempt to tangle the arms of the opponent. The arms can be just as integral to the control that our closed guard maintains on an opponent as our legs.
Hawaii black belt Joel Bouhey, who is a black belt under "Pure Jiu Jitsu"'s Luis Heredia, takes the use of the arms to the next level in his "Falcon Guard". By overhooking the opponent's arm and reaching far across his own waist and chest, he connects that overhooking arm to the opposing arm that is holding the opponent's head breaking their posture. This creates an intense upper body control that can be used to frustrate the person you have trapped and force reactions that can lead to sweeps and reversals from a variety of positions.
In the video below, Joel Bouhey demonstrates the basic "Falcon Guard" control and shows how applying pressure with one's legs at different positions on the torso will lead to unique opponent reactions that can lead to reversals such as the overhead sweep shown below.