I have been running dual 17" monitors on my main shop computer for the past few years. I like being able to have multiple programs running at once in different windows. For example, I usually have my music player up on the left screen, and also use it for things like drawings, articles, or videos. I use the right screen for what is being worked on at that moment, Solidworks, Excel, Square, etc. I also happen to split the left screen's feed to a different monitor that is easier seen on the other side of my desk. This comes in handy when trying to show clients things from my desktop without having to move a monitor. It's also pretty handy cause it can be easily seen from the shop floor, making it handy for schedules, chop lists, and even playlists.
I just received a new to me 30" monitor. Holy crap is it large. The viewing area is immense. Solidworks is insanely large. Small videos are now almost too big.
But it takes up a lot of real estate, so I am contemplating ditching a dual screen setup.
And for the record, it would be a 30" in landscape and a 17" in portrait. Now I am running two 17" each in landscape.