Speakers that are good persuasive speakers use multiple types of appeal; they do this because it works better. If the audience is an audience of one person, then using multiple types of appeal is likely to work in multiple ways on that single person. If the audience is comprised of many people, the usage of multiple appeals means that the speaker is likely to find at least one type of appeal that works for each audience member. It's like fishing with multiple poles that each have different bait. Another fishing analogy would be that using multiple appeals is like casting a wider net.

Matt Cutts uses logos, pathos, and ethos in his very short talk. He uses pathos when he asks the audience about their "wants." I want all kind of things. That's my emotional core talking, but my logical brain says that buying a Bently is probably an unwise usage of money. Cutts uses logos when he flatly says that "the next 30 days are going to pass" no matter what happens. That's a logical, factual statement. While Cutts does make effective usage of logos and pathos, it's his ethos that best sells his argument because he openly tells audiences that he tried, and currently practices, his 30 day "try something new" recommendation. The fact that he does it, shows evidence of it, and shows success from it is far more convincing than any of the logical or emotional arguments that he could make.