Do You Know When You Shouldn't Trap Your Arm?

A lot of the time i kind of have like a four and four rule going on in my head. So if my opponent tries to grab my leg, if he grabs my leg, he's essentially winning te the battle. I know that i'm putting all my limbs to use. If one of my arms is not doing anything, you'll see this a lot with beginners,. They'll be trying to play open guards, but they'll forget to use a hand r yayaa. Well,  you need to have assigned tasks to all your limbs. They need to all be manipulating levers, or working towards breaking a line and rita. You can also create hooks and clamps