I love how this response starts practical and then directs the heart of the matter. I think my approach falls somewhere in-between.

When reading a paper book, I use underlining for individual sentences I want to remember and an extended bracket for a paragraph I want to remember.

Next to the underlined or bracketed text, I'll add a checkmark, star, heart, or exclamation point.

The checkmark means it's worth remembering. The star means it's really worth remembering. The heart means it's something I already know and love to see again. The exclamation point means it's funny or surprising, though I don't necessarily need to remember it.

When I finish the book, I review all the text that's been marked. This helps me remember what's meaningful to me.