Somebody recently asked me if I use split windows in Vim. The answer is of course an emphatic "Yes!", but why?
It actually depends on the work I'm doing. When writing prose, I'll typically use a single window and only split it if I need to refer to another file without losing my place.
When writing code, however, I'm likely to always split windows. For example: a vertical split for a file and its associated unit test, and perhaps later an additional set of horizontal splits for associated view code (HTML templates or similar).
I find it's best to split windows as needed rather than working with a predefined set. It's also useful to take advantage of tabs to organise sets of windows in logical groups. Or illogical -- whatever helps you to be productive!