"I put the glass between the structural members and the members which are not of structure because the joint is the beginning of ornament. And that must be distinguished from decoration that is simply applied. Ornament is the adoration of the joint." ~ Louis I. Kahn
How design elements and materials are brought together reflects the integrity of almost any material composition. Thoughtful selection and assembly of materials clearly signal higher quality than inappropriate or poorly assembled materials. Whether a building, a manufactured object, or a work of art or craft, something judged to be 'well made' invariably organizes thoughtfully selected materials with specific intentions. But how constructed elements are brought together in architecture creates the potential for far more nuanced readings of it than simply whether or not it is well built.
An architectural 'joint' mediates a transition from one element to another. This may occur not only between changes of materials, but also between forms or volumes, grains or textures, architectural elements such as walls and floors, decorative treatments or finishes, lighting conditions, spatial elements such as solids and voids, or even between the expected and unexpected.
One element stands against another in some form. Like two words in a poem that, together, convey a profoundly leveraged compound meaning, adjoined architectural elements may embody a certain poetic expressive potential. Kenneth Frampton notes that "In the last analysis, everything turns as much on exactly how something is realized as on an overt manifestation of its form. This is not to deny spatial ingenuity, but rather to heighten its character through its precise realization." 
 Kenneth Frampton, Studies in Tectonic Culture MIT Press 1995