Done correctly, they can reduce heating and cooling expenses, although not as effectively as a green roof which costs far less per square foot to install. Also, watering a vertical garden is a challenge, as rain tends to fall down, not reliably sideways. Drip irrigation is necessary and frequently monitoring systems are needed.
A green living wall is good advertising. Like the old saying about avoiding a doctor whose waiting room plants are dying, a brown vertical garden loses most of its value. Minsuk Cho who has designed these walls says, "Just like any garden, maintaining a green wall takes commitment. It shouldn't be considered as a building material but more like a pet." They add, a very large and thirsty one.