I think propaganda is necessary to support a war effort (and avoid insurrection). Think of it this way: If you're a soldier and your government tells you to invade a random country with nice people, how willing are you to fight? On the other hand, if your government convinces you that the target country is full of Nazis that eat babies and plan to genocide your people, then suddenly you're a hero if you go kill a bunch of strangers who never did anything to you.

So if you're running a country and you want to invade another country, you better start running the propaganda months, if not years, in advance.

Edit: As another example, take the Iraq War. The US and NATO didn't just randomly invade Iraq without propaganda preparation. Bush was even calling Iraq part of the "axis of evil" for at least a year before the Iraq war.

Propaganda is a very good way to be informed. Precisely because the first law in good propaganda is "you never lie, just do not say anything about what you don't want mentioned". A lie like the weapons of mass destruction in Iraq is going to backfire when people realize, and they will.

I found very useful watching RT propaganda along CNN, or BBC propaganda.

If a group of propagandists fail to state a very important issue while the other do not, let's say they omit the official conclusion about a plane that went down months ago that you accused the other party of shooting down, well you know this party is lying.