Speaking from experience.........

Learning the song or tune by heart so that you can perform it without a crib-sheet gives you a much more personal, intimate relationship with it. It's this which can turn an, on the face of it, trite or uninteresting song/tune into one which grips the listener.
    As far as tunes for dancing are concerned, a bandleader who learns his tunes can rescue a potentially shambolic ceilidh. One who is unable to see over the top of his/her music stand will play blindly on whilst chaos spreads across the dance floor.

Don