It's there for your own use. Those indicate if your operation provides information, does something interesting, or not specified. A good analogy would be GET/POST in HTTP.
I think it matters when you do dynamic mbeans. The behaviour that you get on a Console is dependent onwhat value you specify for the impact. If its ACTION, you would get a UI that lets you change the values for the attributes. Having it as INFO will only allow Read only views. Having ACTION_VIEW is a read/write property.