Streaming is a key technique for building fast web applications, allowing for progressive delivery of UI components to improve performance and user experience. By utilizing streaming with the Next.js App Router and React Suspense, developers can take advantage of out-of-order streaming, which enhances user experience by rendering parts of a UI while continuing to load other elements. Streaming also enables colocating compute next to data origin, reducing network traffic and improving performance, particularly for large sites like Amazon and Google. Additionally, streaming is being used in AI applications with Large Language Models (LLMs) to mitigate slow response times and improve user experience.