Much stronger type guarantees. TypeScript's strength and weakness is how it fits JavaScript like a glove. Elm is a different language entirely, so it can provide much better soundness. It's also a simpler language than JS / TS. TypeScript, being a superset of JS, has a lot of baggage. Elm is pretty small and conceptually simple. Elm is also a framework, not just a language, so it guides your team into building things in one, consistent way (for better or for worse). Finally, the Elm compiler is very good. It produces small, fast build artifacts. Compare the bundle sizes of Elm with the other competing frameworks here[0].

[0] https://github.com/gothinkster/realworld