The advantage of having lots of monitors is that it lets you organize your workspace spatially, rather than having to constantly deal with the cognitive load of manual window management. Tilting my head a few degrees to look at my email client which is _always_ in the same place on my right monitor is significantly faster and more intuitive than having to grab my mouse and click the email icon on the taskbar, or Alt+Tab through a stack of recent programs until I find my email client among them.

There are practical limits, sure. Most people are not going to want to turn their entire body around 180-degrees just to look at another window. Within those limits though I find that more space is generally better.