My experience is that few audit courses when they are working on their first degree. The students at my university were interested mostly in grades and passing courses. They did not seem to give a damn whether they actually learned anything or not.
I had eight office hours every week. Some semesters I never saw a single student until after the Midterm grades were due. No one ever came to me and asked how to pronounce this word in Spanish, or to tell them what something meant in Spanish, as I frequently did when I was in college. I saw all of my professors at least once a month in their office. They were always helpful and glad to see me, and I learned a lot from this.
I have had older students audit my classes, and they tended to learn more than the for-credit students, because I gave them the tests just to show them how they were doing if they asked.