When you are developing an Angular app that is constantly growing in size and needs to be managed very well, you may not WANT to write the same pieces of code in multiple components. In these cases, it is a good practice to write the common logic in a service and use it from different components as and when required. 

Components generally do not fetch or save data from the web RESOURCE or the API and they certainly shouldn't knowingly present fake data. They are supposed to focus on presenting data and delegate data access, like fetching and saving, to a service.

Services are also used majorly for sharing data between different components. Since services are singleton classes, which simply MEANS that they can only be instantiated once throughout the LIFECYCLE of the app, only one instance of a service lives at all times. This can be used to share data between components since all the components have the access to the single instance of the service class.

To create a service in Angular, you can use the Angular CLI command.

The separation of concerns is the main reason why Angular services came into existence. Every service annotates the class with the @Injectable() decorator. This makes the class able to participate in the dependency injection system.