Next.js is a powerful tool for building React applications because of several key features:

1. Server-side rendering: Next.js provides built-in support for server-side rendering (SSR), which helps improve performance by rendering pages on the server and sending fully rendered HTML to the client. This can lead to faster page load times and better search engine optimization (SEO).

2. Automatic code splitting: Next.js automatically splits code into smaller chunks so that only the necessary code is loaded when a page is accessed. This helps in reducing initial load times and improves overall performance.

3. Static site generation: Besides SSR, Next.js supports static site generation (SSG), where pages can be pre-rendered at build time and served as static HTML files. This is beneficial for websites that don't require real-time data and can greatly increase performance and reduce server load.

4. API routes: Next.js allows you to create API routes within your application, making it easy to manage server-side logic and data fetching without the need for an additional server setup.

5. Built-in routing: Next.js includes a file-based routing system that simplifies the organization of your application's pages and URLs, making it easy to create nested routes and dynamic page paths.

Overall, the combination of these features makes Next.js a powerful framework for building modern web applications that are fast, SEO-friendly, and easy to develop and maintain.