We use it in AZ for borderline types that have issues in our dry heat. Cherries, avocado, etc. Serves to slow transpiration and help these types over the hump of getting established. Also useful on rooting cuttings. In the winter we spray the tropicals we have to give them a slight amount more freeze protection.
Its really hard to say how much use these sprays are for us. We have done any side by side tests to see what effect it has next to a control. Its mainly a feel good thing for us right now.