Grated Parmesan is essential in many pasta sauces and is used in quite a few others, even if not essential. However, it is not needed in fish sauces – with the exception of some prawn sauces – nor in plain tomato sauces, such as the Neapolitan tomato sauce, and any sauces using raw tomatoes.
Always use fresh Italian Parmigiano-Reggiano, or Grana Padano, which is another good grating cheese.
Buy Parmesan in whole pieces and grate just before use. Store pieces of Parmesan in the refrigerator, well wrapped in foil. If the cheese becomes very hard and dry, wrap it in a damp cloth for a day and then put it back in the foil in the refrigerator.