I'm sure in the next few years I will be very grateful that I can run the textures at double my resolution with full AA and AF. So pretty! :D
It has nothing to do with Anisotropic Filtering. It's just a brute force inefficient form of full scene anti aliasing that is completely redundant because the game supports adaptive MSAA already.
Basicly FFXIV is using the same offscreen drawing method that FFXI used.
What it does is render the game's 3D graphics (but not the HUD which is drawn to the framebuffer) at 2x the screen resolution into an offscreen drawing surface (this is called Render to Texture in directX and Framebuffer Object in Open-GL) and then scales it down. So if you're running the game at 1920x1080 it renders the game at 3840x2160 and then downsamples it to 1920x1080.
You can't even combine the two because supersampling an image that's already using full scene anti aliasing actually brings back
the jaggies. (try it for yourself and you'll see what I mean)
There is a logical reason for it supporting resolutions lower than the actual screen resolution (high res menus on PCs that can't run the game at high resolutions). But the "double" option doesn't seem to make much sense. It's FFXI's old supersampling trick, except that FFXIV supports MSAA and doesn't need it. Edited, Sep 3rd 2010 10:26am by Lobivopis