Agreed, I wouldn't say XXXX grams of Hershey's chocolate syrup, but I do want to know what size "a can" means.

On the other hand, for things that you would always measure (or need to do to sizes changing) like flour or sugar, I want that in grams for easy measuring. Even chocolate bars, might be easier to just say how much you need since getting exactly what you are looking for might be difficult/impossible.