It's part of a mire poix which is a base for a variety of sauces. This typically includes carrots, onions and celery. Then, assorted spices are added. Bolognese sauce is a good example.
Never heard of pureeing it, but it is common to add celery and carrot to the more standard aromatics of onion and garlic, particularly in winter sauces made with canned tomatoes that can't be carried as much by the flavor of the tomatoes. In todays "pile it on" school of cooking this kind of thing tends to get overused, sometimes to the detriment of clarity and brightness in the final product.
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You could add chopped or diced celery instead.