forRoot function is useful in lazy load Angular application.
e.g. if I import NgbModalModule in appModule and lazyLoadModule(lazy load for some path), this will inject two instance of “NgbModal” service for root module and lazyLoadModule.
may be, There is no problem if you add forChild(without providers) and remove forRoot.
I want only one instance of service through out application(including lazyload modules).