"Explicit" in language design is catch-all term for several different things: https://boats.gitlab.io/blog/post/2017-12-27-things-explicit... (I highly recommend this article.) Defer is still manual and local, just less noisy and burdensome.

Just like every C feature: if you know how it's implemented (and optimized), you will know what is going to happen. All big C compilers already support stack frames and unwinding, so it's not even entirely novel functionality.

While you may object it's not entirely obvious how unwinding is going to be implemented, OTOH in functions with complex control flow it can be easier to understand which `defer`s are going to be run, as opposed to following nested `else` statements, or reasoning about the program state from all `goto cleanup` locations.