I think there are two parallel discussions going on here, one on sacrifice throws, and one on sacrifice falls, both being referred to as 'sutemi' (hmm, would it be sutemi waza and sutemi ukemi?
). In the first, nage allows uke's attack to throw him and out of how he falls regains his balance while causing uke to lose his. I would agree with whoever it was said this is a last ditch kind of approach, obviously just throwing uke rather than being thrown first is probably more tactically advantageous. But good to practice both to be aware of your sense of control (or lack of it
), and in case you need it. It also shows the interchanging roles between uke and nage. In this case, the sacrifice is nage's willingness to take a fall with the goal of eventually throwing uke.
Others I think are refering to just the fall that uke takes, usually I think this is used for breakfalls or other falls that while uke may not want to take, the alternative would be worse (ie, sacrifice your balance, take the fall rather than get your wrist snapped).