FSrealWX Pro Options questions

I have been using FSrealWX Pro for a while now, but there are 2 options I would like more info about. Under the weather tab there is a option named "Set WX from position in NM" what exactly is this setting for? Also what is the setting "weather modes"? There is a normal choice and a auto-mode choice. What do they do?

Also does it really matter what server location to use? I have been using the US location, but is it better to use the DE location?