If you saw that message when patch 3.1.2 came through (like I did) you may have wondered WTF it was talking about (like I did). According to this, the change is to enable projected textures. (It displays the rune rings for spells like blizzard and rain of fire on the ground when they're cast.) Interestingly enough, it doesn't affect the display of spells which are actually called "runes" cast by boss mobs - those are something else....

Do not attempt to adjust the picture. We are controlling transmission. If we wish to make it louder, we will bring up the volume. If we wish to make it softer, we will tune it to a whisper. We can reduce the focus to a soft blur, or sharpen it to crystal clarity. We will control the horizontal. We will control the vertical.

Ahhh that's cool. That option should be on by default anyway.