There were several theories presented in that thread.

The one I find most likely is that this is somehow required to manipulate the weather. Since we are still seeing hurricanes and typhoons being thrown around, it seems this might be their current weapon of choice. Given that none of us really understand how weather modification works, it does not seem unreasonable to conclude that the spraying may play a pivotal role, either defensive or offensive.

As you say though, this also is only speculation.