All of this water retained on the roof will freeze and thaw and causing expansion and contraction and eventually leaks.
The leaves and debris gather around HVAC units and penetrations in this photo. This can cause excess water to be held on the roof, which can freeze and cause membrane contraction. You can also see that the membrane is rippled and detached from the insulation board underneath. All this water retained on the roof will freeze and thaw, causing expansion and contraction and eventually leaks.