The reason not to do it is to limit the non-determinism of the order of execution. In Javascript f1(); p.then(f3); f2(); functions are always cal

The reason not to do it is to limit the non-determinism of the order of execution. In Javascript f1(); p.then(f3); f2(); functions are always called in the relative order f1, f2, f3 and never f1, f3 , f2 even if p had already resolved.