Structured interviews are more formal interview processes where questions are typically created in advance and scoring systems are used to evaluate candidates. Unstructured interviews usually involve less formal conversations with candidates, and the question and answer part of the interview is generally more spontaneous.
A major benefit of a structured interview process is that you know there is greater consistency in the tools used to compare candidates. By using the same format and questions, the interviewer can compare each candidate's approach and answers under the same microscope lens. While candidates sometimes react differently to this style, it works well for an interviewee to show off technical proficiency for a technical position.
Unstructured interviews typically allow for more personal interaction and rapport-building with hiring managers. While the objective of an interview isn't to make a new friend, it does help the hiring manager to see if he would enjoy working with you. You can also give the interviewer a better sense as to whether you would fit into the existing group of employees. Plus, building rapport, such as in sales and service jobs, is often important in the job and should be part of the assessment.
