I was thinking about this one time. From a utilitarian standpoint, having multiple monitors provides a sort of redundancy. If one fails, you'll still have one to work on.

On the other hand, it also depends on your setup. If your setup can easily allow you to manage your workspaces across two different monitors, it might be better than managing everything on one screen. The opposite could be true, and you benefit from only having to deal with one screen and don't have to fiddle with anything.