Atomics guarantee two characteristics. At one hand, they are atomic, at the other hand, they provide synchronisation and order constraints on the program execution.

The atomics are the base of the C++ memory model. Per default, sequential consistency is applied.

I created the facebook group Modernes C++. I see one big advantage in this group.

Since C++11, C++ has a memory model. It is the foundation for multithreading. Without it, multithreading is not well defined. 

In case you are using  promise and future to synchronize threads, they have a lot in common with condition variables. But most of the time, task are the better choice.

The parent of a thread has to take care of its child. The parent can wait, until its child is done or detach itself from its child. But that is not really new. But that will not hold for std::async. The big charm of std::async is, that the parent has not take to care of its child.

With std::promise and std::future, you have the full control over the task.