Here in Australia it is definitely used for cooling, every day in winter that it gets unseasonly warm they come out and blanket the sky, then the next day and onwards it's cold and 3 days after spraying it rains. The only exception is when major events are on they hold off until after or for multi-day events they might spray the last day or a couple of days before. I can't remember the last time something was rained out. They let us have heat waves for sure in summer, the logic of when and why they do or don't do it on a given day in summer is not obvious to me, but again major events seem to be spared rain and heatwaves (but not as consistently as in winter).