When you're a student you can ask anyone a question. As long as you're upfront about not being an expert, it's fine to ask novice questions of world experts because it's easy to believe that you're just genuinely curious. But as soon as you start working, people start to assume that you might have an agenda with your questions.
For example, people are generally cautious not to be critical of themselves or their organizations when talking in public. But when I ask them questions about career switching as a student, they're much more willing to share an off the record point of view. I'm surprised by how few of my classmates send emails or ask for phone calls with people they admire.
Be sure to take advantage of this because you won't have access to this information when you graduate.