What is Elm?
No run-time errors
Elm makes run-time errors a distant memory. It's really hard to crash an Elm web app at run-time. Once it works, it works.
Grow as a developer
Elm is a purely functional programming language, in the same family as Haskell. Impure functional languages include Scala and F#. Since Elm is small, you can learn it to try out pure functional programming, and it's going to be easier than Haskell. Maybe you will like it, maybe not. Still you will get a new experience, and this is going to help you grow as a developer.
There is no free lunch and there are tradeoffs for using Elm. Still, it's worth giving it a try, so give it a try.