Angular's change detection is a fundamental mechanism that ensures the application remains in sync with its data model. Understanding how this process works is essential for developers looking to create smoother user experiences. At its core, change detection allows Angular to track the state of an application and respond to data changes automatically. This means when a user interacts with an application—like clicking a button or submitting a form—Angular can efficiently update the view to reflect the new data, minimizing unnecessary re-renders and enhancing performance.

There are two main strategies for change detection in Angular: Default and OnPush. The Default strategy checks the entire component tree for changes, ensuring that all updates are captured, but it can become inefficient in larger applications. On the other hand, the OnPush strategy optimizes performance by only checking components when their input properties change or when a specific event occurs. By mastering these strategies and understanding how they impact your application, developers can significantly improve load times and responsiveness, ultimately leading to a more satisfactory user experience.

Building responsive Angular applications is crucial in today's mobile-first world. Here are the top 5 best practices that can help ensure your applications adapt seamlessly to different screen sizes:

1. Utilize Flex Layout: One of the most effective ways to create a responsive design in Angular is by using Flex Layout. This library provides a flexible grid system that allows you to easily manage alignment, direction, and spacing across various devices.
2. Leverage Angular Material: Angular Material components are built with responsiveness in mind, reducing your workload while ensuring your application looks great on any device.
3. Use Media Queries: Incorporating CSS media queries within your styles enables you to apply different styles based on the device characteristics, thus enhancing user experience.
4. Lazy Load Modules: To improve performance, implement lazy loading for your modules. This practice ensures that only the necessary components are loaded, minimizing the initial load time and enhancing responsiveness.
5. Test Across Devices: Regular testing on multiple devices will help you identify issues specific to different screen sizes, allowing you to refine your application and ensure a smooth user experience.

Optimizing performance in your Angular apps is crucial for delivering an exceptional user experience. One effective way to achieve this is by leveraging Lazy Loading. This technique allows you to load only the necessary modules when required, significantly reducing the initial loading time. You can implement Lazy Loading in your application by dividing your app into feature modules and defining routes that load these modules on demand. Additionally, consider using Angular's built-in Change Detection Strategy; by setting your components to OnPush, you can limit unnecessary checks, thus enhancing the rendering performance of your applications.

Another essential tip for optimizing performance is to utilize Ahead-of-Time (AOT) Compilation. AOT compiles your application during the build process rather than at runtime, resulting in smoother performance and reduced loading times. To further enhance speed, make sure to minimize the size of your bundles by employing Treeshaking, which eliminates unused code, and utilize tools like Angular CLI to optimize your production builds. Finally, always keep an eye on your app’s performance using tools like Angular Performance Profiler, allowing you to identify and address bottlenecks effectively.