Yes, Andy Kaufman's most influential appearances were on the David Letterman show, because that is what people remember him for. Kaufman reached the largest audience of his career on the Letterman show. Even though he didn't consider himself a comedian, he was still entertaining and funny on the Letterman show, and he gained a large following.
Without a doubt, Andy Kaufman's most influential appearances occurred on The David Letterman Show years ago. None of his other appearances were nearly as memorable as these ones, and the average person would attest to that fact. Kaufman was an overall influential individual in the United States either way, though.
Andy Kaufman made a name for himself on "Saturday Night Live" before appearing on the David Letterman Show. His most famous monologues happened on NBC's Saturday night standard faire in the 1970s. Kaufman was unorthodox, for sure. But he reached a larger audience on NBC rather than with David Letterman.
No, this actor's most influential appearances were not on the David Letterman show. He had many other appearances and shows, that contributed way more to his career than a little time on a late night show. He was a great comedian, and his other work will be remembered even more.
No, Andy Kaufman's most influential appearances were not on The David Letterman Show. While Andy and NBC apparently liked each other a great deal, Kaufman was more known for his appearances on Taxi and on Saturday Night Live. Most people didn't even known who David Letterman was when those appearances were made.