It is a basic ingredient in mirepoix, which is used as a base for a variety of sauces, soups, gravies, and stews. It’s just one component of what is basically just a fresh vegetable mix. You can always just substitute whatever you have on hand or local that fits, just like you would with a stir-fry or fried rice. It’s less about the specific vegetables than it is about the way they are prepared and what they contribute. Onions and carrots add sweetness. Celery balances those with its saltiness. Celery and garlic feel to me like a bridge to the other proper herbs like parsley and thyme that usually go in the mirepoix I combine with a good roux to make gravy.