Owning vs Borrowing

I housesat for some friends and I visited them to see how to take care of the puppy before they left. I only had one question: where did they keep their books? I'd been in every room in the house and hadn't seen a bookcase! And they told me

THEY DIDN'T OWN ANY BOOKS- THEY JUST BORROWED FROM THE LIBRARY.

(photo from here)

I thought that was the weirdest thing! What happens when you want to read your favorite book right then? But then I examined the books I own vs the books I brought to college and I realized that many books I own I don't really love or read or need. If I want to read Frederick Douglas or The Sun Also Rises I can always hop it down the waterfront library and borrow it. I took every book I was sure to read with me to school and they neatly fit on my dresser top.

I'm having a dilemma: purge my books or let them be the one thing I collect?!?