From gaucho (cowboy) camp fires to society weddings, you will always find chimichurri in Argentina, and especially served at asados - traditional Argentinian barbecues enjoyed by families and friends every Sunday. The beauty of traditional Argentinian cuisine is that it's mostly unfettered by complicated sauces and preparation techniques. This is especially true in the realm of the asado. Imagine gauchos on horseback, riding over the vast landscape, the Andes rising in the distance, and cooking over a wood fire with little more than salt and a few herbs to season the meat. This is more or less what remains today, and everyone has their own recipe.
Chef's note: I don't like heavy, over-complicated sauces. Chimichurri is the perfect way to add flavour and freshness to proteins (chicken, beef, fish, pork) without overpowering them.
It's also a great way to add freshness and tang to roasted or grilled vegetables, and makes an excellent marinade. You can use red wine vinegar instead of white vinegar.
A myth about chimichurri is that it needs to be bright green, but you can add finely chopped tomatoes, paprika and cumin if you like. Another myth is that it needs to be eaten straight away, but this is not true - it keeps in the fridge for up to five days.