I haven't done that, but I do use armies parked on the major roads leading out of enemy provinces, in the "softening up" phase of a war. This blocks trade, and if you combine that with a port blockade, you can really cripple the enemy's economy. Just a single unit will do it. I usually use a cavalry unit, so it can quickly retreat if the enemy sends a big stack after it. So that's my form of "raiding." I'll have to try the devastation thing, although I suspect that blocking trade puts a bigger dent in the economy.