This is one of my most used guard attacks. It works across all contexts – sport competition (gi or no-gi), MMA/Vale Tudo, and self-defense, even in a weapons based environment. Note a few things: 1) with his arm locked down and in my closed guard, he is effectively limited in what he can do. Even the dreaded headbutt (a potential issue in closed guard generally) is completely prevented 2) if he tries to free his trapped arm, he gives me plenty of space to hip out to that side and presents me with multiple attacks 3) I have my other hand free to control his free arm preventing strikes, and along with the fact that the closed guard positioning of legs makes it really hard for him to access weapons, I keep safe from almost any offensive thing he can do.
In short, this is a very powerful control, and the sweep that I show flows easily from it, and typically arises from my opponent’s actions to get out of that control. It is one of my favorites.