I do an ACV rinse right after my deep conditioning, which I do every two weeks, between each set of twists. My deep conditioner is very thick, and I like to make sure it's completely rinsed out. Sometimes I ACV rinse while I'm wearing twists. And if I have done a protein conditioner, I use the ACV to knock out the smell (Aubrey GPB--great product, but phew!).
It's also supposed to restore your scalp's pH balance to normal levels, and add shine to your hair.