Modern manufacturing techniques for reduced-fat cheeses are increasingly sophisticated, nevertheless in some situations the performance of these cheeses in cooking is not the same as their full-fat equivalents. A reduced-fat, Cheddar-style hard cheese will melt under the grill, but it will not brown properly. If you want a crusty topping for a baked dish, add breadcrumbs to these reduced-fat hard cheeses.
But in most dishes in which reduced-fat hard cheese is used (such as pastry), you can expect it to perform in much the same way as its full-fat equivalent. When making cheese sauces with reduced-fat cheese, make sure you remove the pan from the heat first, and stir the cheese through at the last minute so it doesn't over-heat. And when using a reduced-fat cheese for sauces, you may also find it necessary to add a little mustard or some herbs to boost the flavor, as it is usually less rich.