Not everyone has the luxury of having such an abundance of tech interviews that they can simply use some of them as practice for the "real" interviews

Feedback, focus, efficiency.

I did about session a day for maybe two or three weeks. I'll compare it to trying to practice by doing real interviews. I got much more detailed and honest feedback from my practice interviews than any real one I've had. I got to practice just the interview type I wanted, algorithms, without doing other things that would come up in a series of interviews (culture, system design, etc). I also didn't have to contact and coordinate with >= 10 companies to get 10 sessions. I just booked 10 sessions.

I used to do interviews for interviewing.io, and it's a bit different. For my work, I'm not going to give any feedback, and will try leave early if it's not going well. When I was being paid for it via interviewing.io, I would give people fairly detailed feedback on what went well and what went wrong, and also answer any questions the mock candidate had.

For me, I'd use a platform like interviewing.io where you'll GET actionable feedback -- most companies won't give you feedback at all, other then "here's your offer" or "nah, thanks anyway"