I’ve noticed that in the past 2 or so years of my education, I take notes during classes but I barely ever use them. I’d often wonder why I even took notes at that point.

The answer to that is that notes function only to make sense of whatever I’m studying. However, notes are not a priority anymore, and I’ll prioritize paying attention in class as opposed to taking notes.

I suppose when studying something, there are 3 things you’ll want to get out of that.

1. understanding
2. ability
3. memory

For me, notes are good (not essential) only and only for the first point: understanding¹. For number 2, practicing stuff is far and beyond the only thing you should be doing. For number 3, spaced repetition is the way to go!

And so to answer the question in the title: not very useful at all!