Factory classes

Can somebody explain what are factory classes good for? As in, "why all this shit"? I have the impression factory classes are yet another suit in the Emperor's wardrobe. To me, they always looked like some bored programmer who needs to keep his job and hates the KISS principle decided to make our lives worse.

Goddammit. I was reading this thinking "Holy shit, decent answers without MEME SPOUTING READ SICP all over the place?" Then I looked at the timestamps.