well Tauriel, its customize-able for one thing (in magos, or world editor), its not global for another, and you don't need regions to use it.
Global weather effects are buggy to use, cause lag, leaks, and are especially annoying to have moving around, picture you want a storm to pass across you're map rather then just appear and disappear, using regions to do that is super buggy because to my knowledge regions don't like to be moved, you can do it, but I don't know how to make it look good. this model is meant to emulate the environmental effects of warcraft 3, its just meant to be used differently. the other 2 tiers above this how ever, are very different compared to warcraft 3 weather. but they needed a weaker tier below them so I made this. some people may find this more useful to them, then just shoving regions around (if you move regions with weather effects, each time you move them they (the rain) all suddenly glitches and either disappears or turns all white for a mili second, this won't happen with my effect because they are particles and will travel with the emitter, but are not locked into the model space, so each particle will finish its birth and death without ever having moved from its original spawn location, making the rain look normal even as the emitter is moved. this creates a ''moving'' rain storm that looks real nice when it advances in distance. something I could not achieve with warcraft3 weather)