This is a big topic, so I can only start to give some positives and negatives:
Positives: it can provide a protection and it "saves" the things that worked: if it worked for a society before to have a special group of soldiers, this can be provided by a social structure: the society will have a group of soldiers and non-soldiers.
Negatives: it can carry on social injustices, such as when in India some people are "untouchables" and they cannot hold any jobs apart from the very worst ones (just as working with waste disposal).
