These aren't recommendations; just things you can do. They serve as reminders for folks who may have habits which no longer serve them. The post-it greeting card and inline book notes aren't contradictory, they're just salient options to different people.
Books aren't for gathering dust, they are for engaging with. Margin notes and underlines is part of that. It's actually pretty great, you often discover different things on rereads.
The notion that books must be kept pristine is from libraries, does not apply to private books.
Greeting cards are looked at once, then usually gathering dust somwhere, and eventually thrown out. Different wheelhouse.
