While "cresc poco a poco" is technically correct, it's not as common in formal musical notation.
Here's why:
* "Cresc" is the abbreviation for "crescendo", which is already understood to mean "gradually increasing in volume".
* "Poco a poco" is a phrase meaning "little by little", which further emphasizes the gradual increase.
Therefore, "crescendo poco a poco" provides a more complete and elegant way to convey the instruction in Italian.