Ok, I can actually imagine useful auto-generated documentation. If the generation tool did some static analysis and listed which exceptions the function may throw, pre-conditions and post-conditions that can be derived from any asserts present, whether it handles nulls and such, that would be useful. Because that's exactly the kind of things I usually miss in a documentation, even where humans made bona fide attempt to actually write it well.
I haven't heard of such a tool so far.
GhostDoc sorta does that, at least for the exceptions which can be thrown directly by the member that it's describing. It can't do that for any calls further down the chain, though.