I have v-sync off for 3 reasons.
1. I don't get any tearing (or other artifacts) with v-sync off (guess I'm lucky)
2. Sometimes my graphic card can't keep up with monitor refresh rate (85 Hz). With v-sync ON, even if it's behind just a single frame, the frame rate will drop to 42.5, if it can't keep up with 42.5 it'll drop to 28.33, then 21.25, etc [framerate = (monitor's refresh rate)/n, where n=1,2,3..., with double buffer]. In my case, jumps down or up from 85 to 42.5 causes microstutters.
Without v-sync, it'll display any frame rate bellow 85 just fine.
3. I'm not sure if AHII supports triple buffer.