Professional voice actors pride themselves on range. So, hiring a few good VAs means you can take care of many, many characters with a small cast (especially if one or two actors are a Man of a Thousand Voices). Oftentimes, this results in funny situations, like two characters played by the same person having intense conversations and heated arguments with each other. The talent is in making sure the audience doesn't know it. If jokes are made about this, it's Actor Allusion. Examples of Talking to Himself include: