I have found that if a piece has more than two parts, you usually still do the repeats. The exception is found in some of the older Scottish collections (Fraser, Skye, Gow) where the A is repeated but the B has variations, so they write out both "B's", so you don't have to repeat. One of my favorite 5 part tunes is Friese Britches and I enjoy repeating each of the 5 parts.