The idea is to allow wind driven rain a wayout of imperfect wall. These vents are only needed for an event like a week long tropical weather system. Its important to avoid mortar blockage of these web holes. Also use a wind/water shield like tyvek behind the exterior to stop wind driven rain from intering the wall ass. Have your best vapor retarder on the outside of the wall assembly and no retarder on the inside of the wall. This includes NO vinyl wallpaper or plastic on inside of the exterior walls to avoid condensation/mold growth inside of the wall assemly. Last keep the inside of the home below 60% relative humidity to help the any moisture that gets into the wall assembly to dry to the inside. This helps prevent mold growth in a humid climates.