Colour, typography, spacing and dimensions provide the foundation. Components apply these rules to elements such as fields and navigation. States matter too: active, disabled, invalid or focused. A collection of attractive default screens is insufficient when real content and interactions differ from those examples.
A component library explains when to use an element and which variations make sense. Examples with long text, different data volumes and small screens expose limitations early. Handover should align design and implementation. Clear naming makes discussions between editors, product teams and developers easier without describing every detail again.
New requirements can call for additional variants. Ownership and rules for adding components should therefore be established. Changes need to account for existing applications. Accessibility belongs in component testing but does not replace assessment of assembled pages. A design system is particularly useful when several pages or products need consistent long-term development.