Comment by drdaeman

If you don’t specify types explicitly they have to still exist somewhere: in someone’s head (in oral tradition of “Ah, yea, those IDs are UUIDs, but not those - those are integers”), or denoted through some customary syntax (be it something more formal like Hungarian notation, or less so - suggestive suffixes, comments, supplementary documents).

They still exist at runtime, and people who work on the codebase need to somehow know what to expect. Having a uniform syntax helps to formalize this knowledge and make it machine understandable so it can assist developers by providing quick hits and preventing mixups automatically (saving attention/time for other matters).

Types may be rarely important for local variables, but they matter for API contracts.