If you can find access to a Solaris machine and bring up textedit - you will see this feature. Each "vertical" file window (in textedit, there is only one file per invokation of textedit), can be split into any number of view ports into the file.
This feature allows the programmer to view simultaneouly multiple sections of code.  E.G. a typedef struct; the calling code passing some arguments; and the called code which you are working on. This saves immense amounts of time scrolling back and forth trying to remember exact details.