If I had some persistent problem or concern I would just bring it up, I wouldn't wait for some scheduled meeting. I guess some managers might not be so easily available.
It's not just the managers. I've worked with great managers who were truly available, but due how busy I perceived everyone to be, I never felt comfortable interrupting things for what I deemed weren't critical issues.
Since we did have regular 1 on 1 meetings, I knew I had a dedicated block of time coming up to hash things out.
What if your manager is in the middle of something? Even if they allow for the interruption trying to help, their mind may still be on the other task, and they likely will try to find the quickest solution to get back to what they're doing instead of the best solution.
If you instead talked about it in your one on one, they can spend more time on it with you.
Since we did have regular 1 on 1 meetings, I knew I had a dedicated block of time coming up to hash things out.