It depends from person to person . Everyone has a different way of learning . Some people like visual representation , some people retain by hearing .
It all depends upon how organized you are and what kind of retention your mind prefers . If you can just mark and study from the books , it’d be much easier and will save you a lot of time .
But , most people want everything at one place , so they make ‘notes ‘ . All the important highlighted information is there . But requires the effort of writing everything down.
Whatever the method of re- enforcement you choose , the only key to long term retention is ‘ REVISING ‘ again and again from the main source .
Hope , this helps !!!