Interface design is fundamentally about matching a flow of information with a real human being.
Some interfaces occupy the entire screen. Others flow along a single vertical column. The question of which approach to use is not aesthetic — it's functional.
The main axis in interface layout is not X and Y. It's time.
This resembles film direction, or the design of fast-food restaurants. Some parts of the space are intended for quick decisions and repeated actions — fast zones. Others exist for reading, understanding, and forming judgment — slow zones.
An interface has fast and slow zones too. Navigation, controls, and status indicators are fast. Content, data, and explanatory text are slow. The layout should respect that distinction; mixing them without thought creates friction.
Page width is shaped by several things at once:
There is no single correct answer. But starting from the temporal structure of the content — what the user does quickly, what they do slowly — gives a principled basis for the decision.