This is probably not a good feature. I think that OP's thread title should be respected.
I agree.
It should not be used willy-nilly. It is especially useful, though, when a thread has, shall we say, "migrated" not to say "derailed" from its original topic.
Also, if the original title was incorrect, inaccurate, obsolete, etc.
Like an election night thread might change from "X is losing" to "Why did X lose?" over the course of the night.