It's mostly about the user experience of the follower, I think (more than the fact that the stories go away after 24 hours).

Snapchat allows a follower to consume all of the stories that they follow in a single stream. You only have to tap quickly to go to the next media item. One can also skip one story and move on to the next with a single swipe.

The fact that everything has to be a direct photo or video from a phone also makes every story feel less manufactured and more genuine. For example, I can go to an NBA player's Twitter account and find that personal tweets and messages from their sponsors are completely mixed in a single feed, while their Snapchat feed is all about their day-to-day personal life (which some find much more interesting).

Interesting. So the key point is that you're encouraged to talk about yourself and not other people or things?

It's the opposite of a link blog, which is what I mostly do; I don't consider my own life to be nearly as interesting to the audience (presumed to be mostly people I don't know) as interesting stuff I can find on the Internet.

It has a different use. If I'm posting links or stuff, it'll go on Twitter. If it's random insights, it might go on both. If it's real life, usually on Snapchat since a lot of people who follow me on Twitter don't care about my day to day activities, moving house, etc. Snapchat is for a closer, more personally involved audience. I unfollow people on Twitter who constantly post personal crap there but expect and enjoy it on Snapchat.

More people use Snapchat actively. They also persist, in that they aren't in a stream that requires the follower to currently be in the app to see.