I am becoming increasingly irritated with interviewees, when asked a question by the interviewer to start the answer with “So….”

Why do they do that,? is there a media training school somewhere that has trained all these people to start the sentence with “So, the reason we have” blah, blah, blah. It is totally un-necessary. Is it supposed to make a difference to the way the information is imparted? does it add anything to the response?

No.