I used Khan Academy to complement my math and econ learning. While the concept of KA is good, with quality practical exercises, I found the videos very inefficient to learn most things.
I understand that it's step by step for the general audience, but KA applies this very slow, remedial structure to everything. The throughput was so bad I quit many series because of desperation.
Some MIT OCW recitation videos are examples of how to do this right. The lesson-giver has surgical precision and gets right to the point. Here's this problem/subject, and here's the relevant knowledge nugget. They'll mention what built up to this problem, which is amazing for discovering prerequisites - but never discuss those in depth. (I believe videos are not the most optimal way to learn in general, but in review and understanding they are very good.)
KA, on the other hand, goes into needless detail and redundance. (It's fine if you mention how demand graphs are relevant, but don't explain the basics of demand graphs again! I'm watching a more specific topic!).
That's how you end up with a long series of videos with sparse knowledge where, after six videos of ten minutes each, you have learned squat and the words "oh, let me use this pen color..." resonate in your head.
You should think of Khan Academy as an average high school lecture course, aimed at an audience of typical students, and with an approach and exercises closely aligned to the standard (frankly, quite uninspiring) USA school curriculum. It isn’t the best possible quality, but it does have 2 big advantages: (1) it is self-paced and available to anyone anytime, and (2) it is consistently okay, setting a quality floor. Human teachers are more variable in quality.
As a society, we could definitely aspire to producing much better materials, but even though I myself would never use it, I’m glad that Khan Academy exists.
I also used kahn academy for similar reason and I think their quality changes depending on the subjects. For me the real value came from their exercises. You get a problem, you don't know the answer, you open all the hints, after a couple of exercises of doing that you see the pattern, and then you have learned that specific thing. When I got stuck was when I watched the videos. It also helps the watch them at 1.5 and 2x respectively, depending on your need.
You can’t compare KA to MIT OCW. Khan Academy is for a general audience and OCW is for an audience of MIT students, who are highly preselected for aptitude to learn this material.
For specialized subjects there is a need for some MIT mettle, but I find many freshman courses are very clear and easy to understand, even more so than their equivalent Khan Academy materials.
Before his controversies, Lewin's Course 8 classes/recitations were a gold standard in Physics learning. He combined intuition and rigour masterfully - along with some brilliant practical experiences.
The recurring theme in many courses (not only Lewin's, but Calculus, Economics, or even Strang's linear algebra) is the great care and preparation of the materials to get the point across. I think this, more often than not, is very successful.
