Angular Dependency Injection is a powerful design pattern that fosters reusability and scalability in web applications. By using a simple injection framework, Angular allows developers to create service classes that can be shared across components, enhancing code modularity and maintainability. This method not only streamlines the instantiation of classes but also promotes better testability, as dependencies can be mocked or replaced without altering the core logic of the application.

Understanding the mechanics of dependency injection in Angular involves grasping how services and components interact within the framework's ecosystem. Services are defined using the @Injectable() decorator, and when a component requests a service via its constructor, Angular's injector takes on the responsibility of supplying the required instances. This seamless flow not only minimizes boilerplate code but also encourages a clearer separation of concerns, which is essential for building reusable code in modern web applications.

When it comes to building high-performance applications with Angular, adhering to best practices is essential for optimizing both speed and efficiency. Here are the Top 10 Angular Best Practices to keep in mind:

1. Utilize Lazy Loading: Divide your application into feature modules and load them on demand to reduce the initial load time.
2. Leverage Change Detection Strategies: Opt for OnPush change detection strategy to minimize unnecessary checks and boost performance.
3. Optimize Template Usage: Use trackBy in *ngFor directives to enhance rendering performance.
4. Implement Ahead-of-Time (AOT) Compilation: Pre-compile your templates and components to reduce the workload during runtime.
5. Avoid Memory Leaks: Always unsubscribe from observables and detach event listeners when components are destroyed.

Continuing with our list, here are the remaining best practices to help you create efficient Angular applications:

6. Utilize Angular Universal: Server-side rendering helps improve performance and SEO by pre-rendering your pages.
7. Use Track By with NgFor: This helps Angular identify which items in a list have changed, thus optimizing rendering.
8. Optimize Image and Asset Loading: Employ lazy loading for images and use efficient formats to decrease loading times.
9. Control NgZone: Use NgZone to run change detection selectively when necessary, keeping the application responsive.
10. Regularly Audit Performance: Utilize tools like Lighthouse to identify bottlenecks and enhance performance continuously.

Optimizing Angular performance is crucial for developers looking to enhance their applications' efficiency. By implementing change detection strategies, you can significantly reduce the performance overhead. For instance, consider utilizing the OnPush change detection strategy which only checks the component when its inputs change, thereby minimizing unnecessary checks. Additionally, employing trackBy in ngFor loops can prevent unnecessary re-renders, leading to smoother UI interactions. Here are a few more tips:

• Utilize lazy loading for modules to decrease initial load time.
• Employ asynchronous loading for images and other resources.
• Minimize the usage of third-party libraries to keep the bundle size low.

Another important aspect of optimizing Angular applications is to leverage the Angular CLI effectively. Using the CLI's built-in production build feature can significantly enhance your app's performance by enabling Ahead-of-Time (AOT) compilation, which pre-compiles the application and reduces the loading time. Moreover, regularly auditing your application with tools like Webpack Bundle Analyzer can help identify and eliminate unnecessary dependencies that bloat your app's size. Remember, continuous monitoring and optimization are vital as you make updates to your codebase, ensuring that performance remains a priority throughout the development process.