The “film” part began as a screenplay competition. Now it’s a place to showcase big name actors and studio films. There still a few low budget indies but they’re being pushed out. I don’t think they even have the screenplay part anymore. And I don’t think anyone ever got a movie made from a script that one.
Houston’s film festival still boasts a market of movies looking for distributors (both American independent and foreign films).
Sundance is about hyping films that will be released to their theaters, their video label, their cable network, etc.
There are a lot of music documentaries that play SXSW but I don’t know how many go in without already having a distributor and release schedule.