Building web applications using Next.js for the frontend and NestJS for the backend API, with PostgreSQL as the database, is indeed a robust and modern architecture. This approach offers several benefits compared to other combinations like React with Express.js. Here's an overview of the benefits and comparisons:

Benefits of Next.js + NestJS + PostgreSQL Architecture:

1. TypeScript Support:
   Both Next.js and NestJS have excellent TypeScript support[1][2]. This allows for type safety across the entire stack, reducing runtime errors and improving developer productivity.

2. Server-Side Rendering (SSR) and Static Site Generation (SSG):
   Next.js provides built-in SSR and SSG capabilities[1], which can significantly improve SEO and initial page load times. This is more challenging to achieve with a traditional React + Express setup.

3. Modular and Scalable Backend:
   NestJS offers a modular architecture that promotes code reusability and maintainability[2][3]. Its dependency injection system and decorators make it easier to organize complex backend logic compared to Express.js.

4. Performance:
   Next.js includes features like automatic code splitting and optimized performance out of the box[1]. NestJS is designed for building efficient server-side applications[2].

5. Developer Experience:
   Both frameworks provide excellent developer experiences with features like hot module replacement (HMR) in Next.js and a CLI for generating boilerplate code in NestJS[2].

6. Database Integration:
   NestJS has robust support for various databases, including PostgreSQL, through TypeORM or Sequelize[2][3]. This makes database operations more straightforward and type-safe.

Comparison with React + Express.js:

1. TypeScript Integration:
   While React and Express can use TypeScript, Next.js and NestJS are built with TypeScript in mind, offering better out-of-the-box support.

2. Server-Side Rendering:
   Implementing SSR with React and Express requires more manual setup, whereas Next.js provides this functionality by default.

3. API Development:
   NestJS provides a more structured approach to API development compared to Express, with built-in support for decorators, pipes, and guards[2][3].

4. Scalability:
   The modular architecture of NestJS makes it easier to scale large applications compared to Express, which can become harder to manage as the application grows[2].

5. Learning Curve:
   While the Next.js + NestJS stack might have a steeper initial learning curve, especially for developers new to TypeScript or decorators, it can lead to more maintainable and scalable applications in the long run.

6. Community and Ecosystem:
   Express has a larger community and ecosystem due to its longevity. However, both Next.js and NestJS are rapidly growing in popularity and have active communities[1][2].

In conclusion, the Next.js + NestJS + PostgreSQL architecture offers a powerful, type-safe, and scalable solution for building modern web applications. It provides better performance, maintainability, and developer experience compared to traditional React + Express setups, especially for larger, more complex applications. However, the choice ultimately depends on the specific requirements of your project and the expertise of your development team.

Citations:
[1] https://www.upsqode.com/blog/nextjs-vs-nestjs/
[2] https://nomadicsoft.io/servnext-js-vs-nest-js-difference-between-next-js-and-nestjs/
[3] https://www.solutelabs.com/blog/next-js-vs-nest-js
[4] https://www.linkedin.com/pulse/building-full-stack-typescript-application-deep-dive-sammartino
[5] https://www.technoexponent.com/blog/react-next-and-node-nest-js-why-are-these-best-for-your-web-app-development/
[6] https://www.reddit.com/r/nextjs/comments/12bhymm/why_nextjs_for_backend_over_express_or_nestjs/
[7] https://dev.to/yakovlev_alexey/creating-a-project-with-nestjs-nextjs-3i1i
[8] https://themobilereality.com/blog/advantages-and-disadvantages-of-nestjs