What does this do?

Like the name, it holds some residual pressure in the bake line after the pedal is released. This can be an issue in a vehicle with the master mounted under the floor. Fluid tends to drain back into the master causing you to pump the pedal to restore fluid back to the wheel cylinders and get a firm pedal. 10#s for drum and 2#s for disc. I don't think they're necessary for your set -up with the right master cyl. / booster combo. JMO
Larry