One thing that working in Silicon Valley taught me is that loyalty is worthless. Companies don't care about you, so you shouldn't care about them. I was a no-show for the first day of work at Nvidia, I took a job with Electronic Arts instead. The pay at EA was less but the benefits were better and I wasn't sure that Nvidia was going to keep me around for more than a year. No regrets.
I've never failed to show up for an interview though. Even if I had zero intention of taking the job I always felt that it was worth the time to gain experience interviewing at as many different companies for as many positions as possible to improve my ability to cope with the social awkwardness of the interviewing process. My dad had the same sentiment, he was let go from a major company and would take any interview that he was called for simply to get comfortable with the job hunt process again.
I've had interviews where I could tell right away the the person doing the interview had zero intention of hiring me, their disappointment was immediately obvious and they struggled to come up with questions to ask. I simply focused on remaining confident and spent the time practicing good interview techniques, looking at a person's forehead, being mindful of my posture, asking a few select questions of my own, etc... I always felt like I got something out of the process and if anything, impressed the person interviewing me such that they might consider me for a different position if one were available.