War is beneficial to the victors, who more or less won the right to maintain their ideas and way of life ... That whole "Greater Good" thing everyone is always going on and on about. Debate and the free exchange of ideas is a wonderful thing ... Until the opposition picks up a sword and tries to force their way upon you.
This question would be answered differently depending on the meaning of 'beneficial'. War is often unavoidable without surrendering a victim nation's freedom or allowing tyranny to overrun the earth. In that sense war is beneficial. But without this necessity, war in and of itself is not beneficial. Were it not for evil people necessitating wars, the world would be a much better place without them.