I’m not going all political here, but bear with me for a second. The United States government was set up with three branches of government, each with their own authority and power: Presidency, Congress and the Courts (Executive, Legislative, Judicial, if you want to get technical about it). It’s a great model, provided that all three both exercise and stay within their given power. Things start going bad when one oversteps and the other does nothing to rein it in.
So what does this have to do with SEO? Put simply, SEO works best when there is a similar distinctions in place.