As a ruler of either the eastern or western empire, what kind of advice would you be getting on why you should try to keep the barbarians happy?

In the year 100 it would only be logical to try to keep protests down. With an empire stretching from Northern Scotland All the way to Rome Italy. If you tried to simply suppress a population that large every loyal Roman Man would have to drafted and sent to the Legions to fight their own disloyal subjects. While if they keep the barbs content they can turn their eye to their enemies such as Boadicea or the Parthians.