Thread:User talk:Reckless Noise Symphony/Categories/reply (16)

With direct searching algorithms, they are, in principle, redundant. They're simply not needed for finding things any more.

But they are useful for grouping and navigating around similar subjects. Your search results can present things with that keyword in it, but it can't show you related things that lack the keyword. For that you need some kind of similarity set to compare and contrast.