An ultrawide monitor is most useful when the layout reflects work roles. Start with one primary action region and add supporting regions only for material that must remain visible. Equal thirds are an option, not a rule.
Give the action the best region
Place the editor, canvas, or document near the center of your natural viewing area. Give it enough width for the working content without stretching text lines across the entire display. A two-thirds primary region plus one reference column often works; a centered half with smaller side references can work for comparison tasks.
Size regions from application constraints
Measure the minimum useful width of each app. Sidebars, tool palettes, responsive webpages, and terminal line length change the answer. Test the longest labels and dialogs. If a region forces horizontal scrolling or hides controls, merge it with another region or move that app to a Space.
Save layouts only after repeated use
Native macOS tiling covers common halves, quarters, and arrangements. Third-party tools can offer thirds or custom grids. Use a saved layout when the same geometry survives several real sessions, not because the monitor has space to fill.
Review pointer travel, neck movement, window readability, and how often a supporting region actually informs the action. A large empty area can be better than a permanently distracting panel.
Project grouping remains separate: it tells you which open windows serve the outcome even if today’s task changes their positions.