I'm echoing what both
cassia and
shadowcat said. Even paying full price, if I had been given a chance to audit a few particular courses I probably would have, if it was at all feasible. Instead, I failed them and fucked my GPA all up. One of those times, I was severely depressed and just coming out of a honest-to-doG nervous breakdown. They were way, WAY beyond what I could handle - both course content and homework/exams. I had an feeling they would be, but my university basically bullied me into taking them right then and there. Taking them to learn the content without worrying about exams and homework grades/deadlines probably would have gone very differently. I also could have just stopped attending class after they sent me back down the rabbit hole and not been kicked out of my uni.
The second was a course I just recently failed - as in, last week. I signed up at a (legit) online uni so I could finally finish the degree I started years ago (see above - I was kicked out after my GPA fell too far). I signed up for one of the required general courses at the urging of my advisor, even though I knew I was going to be completely lost. I was right. About 4 days into it, I couldn't make heads or tails of anything. I bombed the quizzes and got shot down by my professor on the required "discussions" (a major chunk of the final grade). Add in some major life stress and I shut down. I don't know if I would have learned much of anything auditing the class, but not having the quiz grades or being penalized for not "discussing" things the right way would have taken a major load off. I'll have to retake it eventually, and I'm hoping that learning via coursera/youtube/other books will help me eek though it next time.
"Selfishness is not living as one wishes to live, it is asking others to live as one wishes to live." - Oscar Wilde