For small projects, dynamically typed languages are fine. but as the project grows bigger, the static typing will help and will make thing simpler.
As the project grows, refactoring will be an issue. Static typing will make it simpler to refactor.
Tests are smaller.
Reading the code will be easier since you know the contract of functions.
Fewer runtime errors since most errors will be caught at compile time. Also, the stronger the type system it is, the more it will be caught at compile time.
I don't think it slows me down that much. It's a little more typing, and there is compile time overhead. In some cases, you have to work your way around the type system. But at least with Scala, I am confident my code will work as intended as long as it compiles successfully. I spend less time debugging in runtime and writing tests. I think static typing might save time in the long run but not short run.