You can stir the pot to see what's in it. Sometimes you find out some things you didn't know.
You can stir the pot so somebody else can see what's in it, if you think there are things people need to know. Instigating and agitating can reveal things, and it's much more effective than just telling them. If they see it for themselves they'll believe it.
Or you can stir the pot just for fun, because you want to get stuff floating around. That's the worst reason, but the most common one.