I have never searched by bookmarks before so i don’t have that good of a grasp on how it functions.
Bookmarks are used to keep track of fanfictions/series, but are different from the marked for later list. Personally I use bookmarks for fics that i really enjoyed reading and want to read again. Marked for later is a ‘to be read’ list for me. Users can add their own tags alongside the authors so they can keep track of them better. I will go over them more later on.