Shared module provides a service to lazy-loaded module

The lazy loaded scenario causes your app to create a new instance every time, instead of using the singleton.

Lazy loading is the best practice of loading expensive resources on-demand. This can greatly reduce the initial startup time for single page web applications (SPA). Instead of downloading all the application code and resources before the app starts, they are fetched just-in-time (JIT), as needed.

The eagerly loaded scenario your app to create a singleton, instead of creates new instance every time.

Explore in depths about Lazy loading - https://angular-wbecxz.stackblitz.io/partners

 

For Diagram Application Injector

https://www.code-sample.com/2018/05/lazy-loaded-module-angular-5-and-4.html