Essentially every single web application being developed out there gets inputs from its users. Maybe it’s got a comment feed with a few text boxes. Or maybe it has some sort of calculator with different inputs and sliders. Of course, there’s almost always the login page. Yes, the email and password are inputs as well.
HttpClient is an evolution of the existing Angular HTTP API, which exists alongside of it in a separate package, @angular/common/http. This structure ensures that existing codebases can slowly migrate to the new API.