KDE Visual Design Group/KirigamiHIG/Principles/ContentIsKing
When Space is Limited, Content is King
Especially on mobile devices, even though their screens are getting ever larger, screen space is still limited. Additionally due to restrictions in input methods, those devices are especially useful for browsing and consuming content, and less useful for producing content.
Based on that, one of Kirigami's design principles is "When space is limited, content is king". This means that it aims to leave as much screen estate as possible to the content, by showing static user interface elements for navigation and executing actions only when needed, and making them occupy as little space as possible (without sacrificing cpmfortable interaction).
When designing a Kirigami user interface, make sure to maximize the screen space available for the content.