Often a piece used in the early stages of playing the
piano.
Because of the trip-l-et (triplet), or 1,2,3 feel of Mer-ril-ly, it can be difficult to count for students, who, just mastering 1,2, 1,2, completely lose it when counting 1,2,3,1,2,3.
I'm not sure what peace that inspires, especially for the harried piano teacher.