During Q&A in English, "well" and "uhm" are two ways to begin a reply.
If you known the answer, you begin the reply with "Well... ". This creates a pause such that the speaker can arrange his thoughts and construct the clearest answer with good sentence structures. If you aren't sure of the answer, but want to guess anyway, you begin with "uhm...".
In Japanese, my opinion is that it's natural to begin a response to a question about which you are unsure of with "あの、... blah blah.".
But, how do you begin to reply to a question about which you are confident? While I do know the answer, I want a pause so that I can arrange my thoughts. If I lead with "あの", it could look like I am taking a guess.