The following is a modified excerpt from Applied Qualitative Research Design: A Total Quality Framework Approach (Roller & Lavrakas, 2015, pp. 56-57).
Strengths
The potential advantages or strengths of the in-depth interview (IDI) method reside in three key areas: (1) the interviewer–interviewee relationship, (2) the interview itself, and (3) the analytical component 
of the process. The relative closeness of the interviewer–interviewee relationship that is developed in the IDI method potentially increases the credibility of the data by reducing response biases (e.g., distortion in the outcomes due to responses that are considered socially acceptable, such as “I attend church weekly,” acquiescence [i.e., tendency to agree], and satisficing [i.e., providing an easy “don’t know” answer to avoid the extra cognitive burden to carefully think through what is being asked]) and nonresponse, while also increasing question–answer validity (i.e., the interviewee’s correct interpretation of the interviewer’s question).
An additional strength of the IDI method is the flexibility of the interview format, which allows the interviewer to tailor the order in which questions are asked, modify the question wording as appropriate, ask follow-up questions to clarify interviewees’ responses, and use indirect questions (e.g., the use of projective techniques) to stimulate subconscious opinions or recall. It should be noted, however, that “flexibility” does not mean a willy-nilly approach to interviewing, and, indeed, the interviewer should employ quality measures such as those outlined in “Applying a Quality Framework to the In-depth Interview Method.”
A third key strength of the IDI method—analyzability of the data—is a byproduct of the interviewer–interviewee relationship and the depth of interviewing techniques, which produce a granularity in the IDI data that is rich Read Full Text
Because we are conducting qualitative research. Not qualitative let’s get a few warm bodies around the table for our face-to-face focus group, but actually research methods that, like all research, demand certain protocols that address potential biasing effects. One of these is nonresponse. The warm bodies in our group discussion may make the moderator and client observers feel great – Thank goodness, someone showed up! – but the uncomfortable reality is that the people who chose not to participate – or were never contacted by a recruiter and asked to participate in the first place – greatly affect our research outcomes. Indeed, the trajectory of a group discussion 
Research Design Review 