Question Multi monitor gaming support


Forgive what may be a topic that is already covered, links appreciated.

I have used (2) monitors off and on for years. I note that in most of my games, they did not support multi monitor, in particular just two, very often. I know in many games you can do (3) and such as racing games can benefit greatly from said.

When using (3) monitors, how does this effect framerate? In other words, if you have (3) of them hooked up does it see them as 3X (set resolution) for instance 1080p, or does it see them as a widescreen resolution?
I know that when you increase the resolution that it creates a higher demand on the graphics card, so it would go to follow that having (3) monitors set would be taxing the card more, and thus causing a drop in performance/frames. Is this indeed the case?