-A noise one makes instead of a sigh.
-A noise one makes that indicates
apathy towards whatever is occurring at the moment.
-A noise one makes when one is
bored or uninterested.
-It can also be used as a response to something when there is no answer for it, or if you do not know the answer to it.
-It could also show ones agreement with another
person when one is not in the correct mindset to answer with a word or sentence.