A major benefit is the ability to quickly understand code you didn't write because you have the ability to 'go to definition' or 'find all references' which wor

A major benefit is the ability to quickly understand code you didn't write because you have the ability to 'go to definition' or 'find all references' which works across multiple files. On top of that once you understand the code and need to modify it you can quickly refactor across multiple files instantly and with a high degree of confidence. Types are not a substitute for tests, but they eliminate an entire class of bugs that are screened out at compile time. That way you can focus your tests on functionality and not silly mistakes.