I can confidently say that none of my technical interview practice has ever transferred to a useful skill in the job role, but I can confidently say it has helped me land jobs. Not using it definitely makes me forget it.
You don't forget, but you do fall out of practice doing what are essentially competitive programming exercises.
When you're in a situation in front of a whiteboard with 15-45 minutes to craft some algorithm it makes a ton of difference whether or you've been practicing.
Because these skills are use-it-or-lose-it. They will be LRU'd out by the skills you will actually use every day. I guarantee at your next job you will not have to roll your own red-black tree from scratch...