Proper ventilation has intake (vented soffit) and exhaust (ridge vent).  When an attic is properly insulated, baffles are required at the eaves in the attic in order to maintain the air passageway so that the attic is adequately vented.  Otherwise, an improperly vented attic can lead to moisture/mold issues and degradation of roofing system components as well as insulation R-Values.

Homeowners that have a minimum insulation level in the attic equal to R-19, reflective roof shingles and proper ventilation can experience up to two-thirds less solar heat gain than those with characteristics such as little to no insulation, dark roofing shingles and no attic ventilation. 

• Intake down low (soffit)
• Exhaust high up (ridgevent)
• Proper baffle install 
• Optimal attic ventilation

Baffles maintain an air passageway up and over the insulation so that it can exhaust up top at the ridge vent. 

The baffle also serves the purpose of preventing wind washing of the insulation which makes it less effective.

Baffles are only required if the soffit has intake holes/air passageways that lead into the attic and the area above the living space.