Do we need to return always a `SmartPromise`?

[Byloth]

This library introduces the concept of SmartPromise, a Promise object that allows developers to programmatically know if it's still pending or has already been resolved or rejected.

So... Do we need to return this type of object for every internal methods provided by the library?
This specific behavior will produce a small amount of overhead (both in terms of time and memory space) for each asynchronous method called.

Is this acceptable or would it make applications slower?
Some performance tests need to be done.