What is the difference between affable and benevolent?

Although an affable person will often be benevolent as well, that is not always the case. An affable person has a friendly manner. A benevolent person has good intentions toward others. But one can have a friendly manner without really having good intentions. Some people like to appear to be friendly in order to be popular (politicians, for example) while they may actually be quite selfish in their motives and may not be particularly benevolent.