Fewer window switches, more focus
Comparing a document against reference material, or keeping a chat window open while you work, are classic cases where split screen removes the need to constantly alt-tab or click between overlapping windows -- both stay visible the entire time.
A larger display makes it more useful
Windows supports up to a four-way split for people who want to arrange several apps at once, and the bigger and higher-resolution your screen, the more comfortably several windows can share it without feeling cramped.
Frequently Asked Questions
Can I split the screen into more than two windows?
On Windows, yes -- you can snap up to four windows into a grid layout, and a larger monitor makes arranging several windows at once much more comfortable.
What if my split-screen option seems to be missing?
On older operating system versions the feature can be limited or absent, so updating to the latest available system version is usually the first thing worth trying.