It's a cpu instruction which is pretty demanding on your cpu. To my knowledge it's not used a lot. If you do not use AVX you can run a higher clock. To determine if your overclock is stable you run benchmarks to test it, you don't want them to use AVX because that draws a lot of current and causes heat issues. If you set a high AVX offset, thereby limiting the frequency of your cpu when avx is used, the clock will collapse to the your cpu frequency minus the offset and causing performance issues. To be sure this does not happen, you can disable AVX in windows.