Traditionally it helped less familiar posters see who should be taken seriously when ad hominems and slander is spread out there. For example, I have a crowd of jealous admirers who run from sub to sub hating and making up random lies about me, but 80% of them are deep in the red so folk know not to take their bullshyt serious.
Now that reds can neg as much as they want though, it lessens the value of rep cause they'll just sit around negging all day long now to get back at the respected posters they've been stalking.