Isn't using the sessionStorage basically the same as 'storing' a value in some Angular (injectable) service?
When the browser tab refreshes or closes, both are gone. Otherwise the value will be available in both cases.
Am I missing something here?
sessionStorage is not 'gone' when you refresh the tab. That is a huge difference to a service since you can store i.e. a user authentication / refresh token in sessionStorage and keep using it.
Another use case can be lookup data from your database. GET data once, store in sessionStorage, use again later.