I dogear my own books (not borrowed, obviously) but not to mark my place, just to highlight, almost always in non-fiction.

Dogearing acts as a reminder to Future Me when rereading that there's something on this page which drew the attention of Past Me.

Above and beyond the information on the page, this is a reminder about what things were new or intriguing to Past Me, giving insight to how I have (hopefully) changed over time.