These sounds are very important means of communication between mother and her offspring. Cubs use it to demonstrate need for food, social interaction or playtime.
Grown dogs make these sounds in front of a dominant specimen or an animal that is threatening, in order to emphasize that they are tiny, submissive and cub-like. Beside this, these sounds can be a call for help in moments of extreme danger, physical, as well as mental, suffering.
Short frequent whines with confident body posture signifies expectation, excitement or pleasure. Some dogs will "howlingly yawn" instead, or even do one after the other.