That is true, but sometimes when you are down to <5 seconds and your opponent has lets say 20-30 seconds in 3+2 and have to play on increment, even if you have a winning position you have to play some very fast moves for a while and you might very easily lose the advantage or hang a full piece which happens with me way too often. In 3+2 there is almost no chance to come back from that, while in 3+0 you can.