And the reason it’s a warning and not an error (like in C++) is that it’s actually possible that the object can respond to such a message but the compiler doesn’t know about it.

It was incredibly useful in the olden days. The NeXT/Apple ecosystem leaned on it heavily.

We have new ways to approach problems nowadays, so it may be fair to say that object-oriented programming is a relic of the past. I mean, it is telling that Smalltalk, Objective-C, and Ruby are the only languages to ever go down that road. Still, if you are using an OO language, then it makes sense to lean into OO features. Otherwise, why not use a language better suited to your problem?