First off, yes, the environments in this game are often beautiful and amazing. Not denying that. The changing weather also adds to this. However, weather states such as rain, chew through performance and cause things to be horribly laggy. I personally can drop below 20fps whenever rain starts. Combine that with going into a high activity area (like a major city to pick up/turn in pledges), and I'm lucky if I don't get times where it either: a) freezes, gives me a frame or two, repeat; b) chucks me into another loading screen, or; c) crashes the game.
I know a lot of people struggle with performance in this game and I feel that being able to disable weather would actually help. This would of course be in the settings of each player and would be individual, ie. won't affect those that don't want to use it. Just like changing water reflectivity. (But IV1IVJA, your 'mersion ruins mah 'mersion!... -_-)