Editing Decorator pattern (section)

=== Architectural relevance === 
Decorators support a [[Composition over inheritance|compositional]] rather than a top-down, hierarchical approach to extending functionality. A decorator makes it possible to add or alter behavior of an interface at run-time. They can be used to wrap objects in a multilayered, arbitrary combination of ways. Doing the same with subclasses means implementing complex networks of multiple inheritance, which is memory-inefficient and at a certain point just cannot scale. Likewise, attempting to implement the same functionality with properties bloats each instance of the object with unnecessary properties. 
For the above reasons decorators are often considered a memory-efficient alternative to subclassing. 

Decorators can also be used to specialize objects which are not subclassable, whose characteristics need to be altered at runtime (as mentioned elsewhere), or generally objects that are lacking in some needed functionality.