It's a fairly tiny niche of the community which is covered by this suggestion but worth discussion nonetheless, in my opinion. There are a number of us who use dual (or more) monitor setups with our computers for various reasons. I, for one, use my other monitor as a home phone, messaging hub, and tv when the occasion arises. In game, I use it to read guides, look up locations on youtube and maps, and coordinate with third party communication programs. This kind of setup makes mutlitasking while gaming much simpler for me. (Plus, I don't have to fidget with multiple devices.)
The problems I have here are twofold:

1. I cannot use my cursor outside of the screen while playing. I have to alt+tab to interact with my other screen. Being able to use an the cursor outside of the game whilst it is running would make the game a little less laggy because I could more easily play the game without map addons, that take up a good bit extra ram and vram. Being able to freely move the cursor would negate quite a few performance issues with regard to lag on both the machine side and network side.
2. I cannot use my other screen for sound output because I can't choose the output device with the sound options. Being able to use the sound output with my other sound devices can make communication somewhat easier and make it less disruptive while I'm trying to play. This last comment can be a little confusing, but by being able to use different devices to play sounds I can more easily distinguish where it came from and what program it was.

I understand this is a very minor concern for the development team, but it is a small consideration that will go a very long way with me and others who use this kind of setup.