Having a type-based system in JavaScript is essential if you want to build enormous projects. If you've ever written more than 100000+ lines of javascript for a project, you'll realise how quickly JavaScript becomes messy and how difficult it can be to find a bug. It's even worse if you didn't write that 100000+ lines of JavaScript and have to debug somebody else's JavaScript.
If you compare it with the ease of debugging in a Java project for example, you'll understand why enterprise in general is hesitant to use JavaScript for large projects. TypeScript is definitely a step in the right direction, ES6 even more so if we want to start building true abstract components that can be re-used. If it makes JavaScript a more sustainable eco-system to use in the enterprise, everyone wins.
Also, IDEs do much better understanding your code if there's a type-based system which gives you much better tools to do push-in refactoring, renaming things, giving you hints about variables that aren't being used or using variables that doesn't exist or when you assign values to variables that shouldn't be taking that value, etc.
Personally I prefer Dart's optional type system, it feels much more powerful than TypeScript and if you want to ditch the types to get a prototype out quicker, then you can do that without having to declare the type as any.