It's only secondarily designed to allow self-censorship. It's primary function is to give the Ignorer a false sense of superiority and control over the Ignoree. And the real benefit is low-cost self-mitigation of member conflict. No external moderation resources are required. Working entirely alone the Ignorer can suddenly feel righteously vindicated that they finally got the better of the Ignoree, without the Ignoree ever noticing anything at all has changed. So everybody wins.
Ever notice how many members feel the need to
publicly announce that they are putting another member on Ignore? That's because they fear the Ignoree (and everyone else reading along) may never even notice that he or she has been "controlled", and have thus lost the battle of perceived superiority.
The winner can't feel he won until everyone else knows the loser didn't, right?
Ken