I believe that in order to have an effective interview, there must be some structure as to what is expected, and what will be asked. There has been a lot of studies around the results of unstructured versus structured interviews and their effectiveness. With unstructured interview, as a hiring manager you leave a lot of room for unconscious bias to enter, often leading you to hire someone similar to you rather than who might actually perform on the job better. I believe that there should be a system to judge candidates on a level playing field by being able to score answers comparatively.
I have done many interviews in the past and I would say that the majority did not feel to be very structured, many feeling just to be conversations with very little detail about myself being explored or asked about. I definitely did struggle more however in the more structured interviews as a result because of the difference in questions that were asked. In the unstructured interviews there was a lot more questions that would be asked that I felt were not very relevant to the job and in the more effective interviews they had asked about previous experiences that could be indicative of on job performance. Although these interviews are much more thought provoking, I believe that it gives you a better sense of what is expected of you and the experiences that you might have on the job rather than a causal conversation. I feel that this also gives you the best and most prepared candidates. I would advise most employers to take this more structured approach towards interviews.