There's so much redundancy built into the language if you don't. Imagine:

    std::shared_ptr<T> p = std::make_shared<T>();

Then replace T with a very long type. And that's not the most verbose example, just an early one that popped into mind.

Then you have lambdas. Imagine assigning a lambda into a stack variable without auto, also keeping in mind that std::function adds overhead.