Having been on both sides of this, most investigators basically have told me most people have nothing of interest to say. For the ones I have given, there has just never been anything I knew of interest. As far as I know nobody was having an affair, bankrupt, spending beyond there means involved in criminal activities etc. etc. A lot is just to verify that if you said you lived at address 105 street lane, you actually lived their, stuff like that. My first clearance was the worst, I had lived in so many different places over the previous 15 years, that figuring out where and whom my neighbors was took forever, not to mention foreign trips I could not remember any details of. I think I re-did the form several times, after the reviewers kept coming back with, that part is filled out wrong, where exactly were you for the month of August in 19XX, when did you go to Canada, Europe, with whom, who did you see. etc. etc.