One difference between benign andand benevolent is that benign means "not harmful" while benevolent means "helpful". For example, "their intentions are benign" means that they do not intend to hurt you, but does not necessarily mean that they intend to help you. Benevolent, in contrast, refers to something or someone that is affirmatively helpful or generous towards you.

In the U.S people are not typically described as benign or benevolent. Most commonly you hear the word "benign" associated with tumors, or skin growths that are unusual. If it is benign, then it is not cancerous. "Benevolent" is commonly used to describe charitable organizations, and may even be in the name of the organization. I have also heard it used when talking about the intentions of non-human entities in the realm of the occult and aliens. Whether you believe that or not, that is a fairly common usage.