In earlier eras there was composed music, which was always played from the score, and there was improvised music. Since performers were almost always composers as well, as Mr. Hough explained, for a pianist to play, say, a Chopin ballade from memory would have been considered the height of arrogance, as if the pianist were suggesting that he had composed the piece.

http://www.nytimes.com/2013/01/01/arts/music/memorizations-loosening-hold-on-concert-tradition.html?pagewanted=all&_r=0