If you are writing small and simple apps it will give you more velocity and much less boiler plate.
As apps grow it becomes harder to keep track of things and can quickly grow into a mess. You then start to need external tools to give you the features of a strong static type system.
Also from a web point of view you don’t want the website to crash and burn with every error. JS will power through things like invalid types. Imagine if any error caused the website to just stop.