Are you using a netbook and have not much screen real estate? Then wether it is a mail client or web browser or news aggregator using it in full screen mode gets you more content visible. Less space is wasted for menu elements and window decoration.
In Liferea press F11 or select "View" -> "Fullscreen" to enable full screen mode.
If you want to save even more vertical space consider hiding the toolbar by enabling the option in the preferences dialog.