Perhaps, maybe, and so on.
It is an indication that I might do something, but by the very fact that I use it in conversation I am in fact indicating a certain reluctance to do what was asked - that is why I say "perhaps".
Or, it indicates doubt on my part, and occasionally a sort of disinterestedness - my lack of interest regarding the subject at hand.
Surely, it can also be used to show a sort of intellectual care and responsibility - to point out the uncertainty of one's views.
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Yet another answer is that it allows for possibility. The denial of certainty is a fall into doubt, but an opening of that space we call "maybe".