> it seems like it really means "stack variables that go out of scope are deallocated"

And the destructor, if any, is called. That means you can bundle automatic cleanup action in the destructor, no need for goto: cleanup, @try/@finally or some other sort of "manual" cleanup, the cleanup is implicitly set up by, well, the setup.

The ability itself is by no means unique to C++ (even amongst oldies, Smalltalk has BlockClosure#ensure: and Common Lisp has unwind-protect) but a surprising number of languages still don't have such a capability, and it's a pretty neat consequence of C++'s memory model.