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.

Compilers should be responsible for any and all optimization, making the programmer do it by hand is Bad and Wrong.

And this is why Every OS Sucks. Let's All Capitalize Words We Read In The Jargon File! LUSERS!