Firstly, it is easy to get started and low commitment.
Then there are the pragmatic things that will make developing that bit easier.
- Compile time errors. Fewer bugs make it to run time, and errors are quick and easy to spot, especially if your compiler is paired with an IDE that has good Typescript intellisense, like Webstorm.
- Better intellisense. Interfaces and class definitions mean your IDE can suggest/autofill available properties and methods. C# devs used to Visual Studio and ReSharper will be well acquainted with how much time this saves.
- Code readability. Whether your own old code, or someone else’s, it’s way easier to work out what’s going on when you have explicit typing.