renting at blockbuster made sense. You could watch a movie unlimited times within a 5 day period for $1.99, versus purchasing the video for $29.99.
renting at Amazon Kindle doesn't make sense. You could pay $9.99 to rent a digital version indefinitely (or until Amazon loses the rights to rent), or you can pay $6.50 to buy a paperback version that you have second sale rights to.