Yes, actors' talk show appearances often do make people want to see movies. If the actors who visit these talk shows are funny or personable enough, it may make make moviegoers more likely to see their films. These segments often also show movie clips that may entice viewers to watch them.
I guess most TV shows spend a lot of money to invite famous celebs to their show. Emma is one of the most likable females of our time. She is beautiful, humble, and hilarious. Talk shows make money from advertisers based on audience size, and audiences tune in to see stars, so guests on daytime and nighttime talk shows are paid accordingly.
Yes, the whole point of a celebrity appearing on a talk show is to promote their latest movie, book, album, or whatever project they just completed. Talk shows are fun to watch, but celebrities don't show up just for the fun of it. They show up to generate excitement and build up sales of movie tickets, books, or CDs.
Sometimes an actor appearing on a talk show is very engaging. Especially on Fallon because they do things like whisper or lip sync and that gets the audience engaged and often provides extra appeal for folks to want to see the actor's next film. I remember Emma Stone's lip sync challenge with Jimmy, and while it didn't make me want to see that awful Hawaii movie, it did make me like her.