You'll have noticed that although I learned more from my home study course, I still did a four-year course at college. I couldn't get recognised exam certificates from correspondence courses. That was the main benefit.
If you want to study genetics and you don't even know what a gene is, you obviously don't know enough to plan a syllabus for your home study.
You get a useful skeleton outline from your lectures. Using my book about exams you will learn how to improve on the skeleton, but you need one to improve on!
At home you don't have a chemistry laboratory or a machine shop or volunteers to practice dentistry.
Apprenticeships let you learn about real life from an employer. Schools and colleges have labs and workshops for you to do your practical work.
Lecturers don't know as much about practical work as an employer would. I hated doing chemical titrations because they took such a long time.
Then I noticed that one of my classmates took about a quarter of the time, with greater accuracy. He worked during his holidays at a chemistry lab. He showed me the tricks and I was soon flying through my titrations too.
Even if you do have a machine shop at home, you'll be taught safe working procedure in a conventional course. That could save you from being a cripple for the rest of your life.
Instant Feedback
When I was about to hold a chunk of metal with a rag wrapped round my hand to give me extra grip, my lecturer yelled a warning. That probably kept me from losing my hand.
Even if you're learning something safe like oil painting, you can learn faster with instant feedback from a lecturer strolling around behind the students.
Oh, you could take a digital photograph of your oil painting and shoot it down the line to an instructor, but she could be having a meal, or even be asleep if she is on the other side of the world. So you still won't have instant feedback.
Writing essays works fine.
Conventional courses for abilities
It seems that conventional courses win out when you want to develop an ability, unless your parents already have that ability to pass on to you.
Knowledge courses
Of course, there are knowledge courses such as English, Philosophy, History, Anthropology where you don't have a practical syllabus. These are ideal for home study, and perfect for using an essay as a tool. More and more Universities offer online courses. You can get recognised certificates with home study. You just need to be good at writing an essay (see my free report) and a few other exam techniques to succeed.
Even technical courses have lots of theory. University extension courses allow you to study the theory online. Then you just go to college for your practical work.