What's the difference between a floor-standing tower and a bookshelf speaker plus subwoofer?

Floor-standing towers pack multiple woofers and often passive radiators into a tall cabinet, so they reach lower and play louder without a separate sub in many rooms. Bookshelf-plus-sub setups can be more flexible to place and tune, but towers like the Klipsch Reference and Polk Monitor XT lines are designed to deliver full-range output from a single pair, which many verified-purchase reviewers prefer for simplicity.