Answer 1

Why not?
It helps if you note down small things you come across like less used features, better way to do certain things, understanding confusing concepts.

So when need to revise or check certain things you will check your notes rather then searching, researching for it again.

https://www.quora.com/Should-I-take-notes-while-learning-how-to-code
https://www.reddit.com/r/learnprogramming/comments/2809h3/how_can_i_effectively_take_notes_while_learning/