“It is not likely that anybody could question the necessity of ornaments. They are found everywhere in music, and are not only useful, but indispensable. They connect the notes; they give them life. They emphasise them, and besides giving accent and meaning they render them grateful; they illustrate the sentiments, be they sad or merry, and take an important part in the general effect. They give to the player an opportunity to show off his technical skill and powers of expression. A mediocre composition can be made attractive by their aid, and the best melody without them may seem obscure and meaningless.”
— Carl Philipp Emanuel Bach (1714-1788) in Versuch über die wahre Art das Clavier zu spielen (Berlin, 1753)
(☞ found on dolmetsch.com‘s music theory online: ornamentation)