#3 usually comes up on most "how to interview" guides as something you need to do, and so I used to ask a question just for the sake of it. I figured out late into my career why this is so important and why I always liked candidates who had a ton of questions for me:

Top performers usually have many career options and are very picky about the company they're going to join. Asking questions about the company shows that (a) you have other options and are "interviewing" the company for fit and also that (b) you care where you work. These are both very good indicators of a great employee.