i dont have very specific one, but as quick thinking, i would say a " quick login panel" for example.
it would be a component that can be in “notLoggedYet” state with login form displaid login password inputs and signin button
or it can be in “loggedIn” state with a disconnect button
everything else in the component could be same
mainly it is easy conditionnal display of components according to state
but adding or removing elements in ui impose sometime to change the layout too so
of course you can do it by code, but need an easy, no boilerplate code way of handling it
maybe well thinked macros could do the trick