Suit yourself.

It is just one tool among many for the acquisition and retention of knowledge.

I like used books with notes in it. It's interesting to see what someone previously reading felt was important or to glimpse into the past life of book itself.

This made me remember a time I checked a book out from the library and found lots of little notes written in Chinese characters in the margins throughout the book. Most if not all were, I assume, translations of words. It was quite nice - they had wonderful penmanship.