It is as true for oil as it is for wine that filtering strips it of some of the substances that carry flavor. Wines that are meant to develop in the bottle may profit from the presence of those substances, but unlike some wines, no olive oil gets better as it gets older. The dark vegetable water which, because of its weight, drops to the bottom of a bottle of unfiltered oil will eventually develop undesirable odors and befoul that oil. If you can get oil that is only a few months old, an unfiltered example will deliver fuller taste, but if it is much older, it is safer to choose one that has been filtered. If you have a bottle of very good, expensive oil that has thrown off a murky deposit, use the filtering method that one of my producer friends himself employs: Put absorbent cotton into a funnel and strain the oil through it into a clean, dry bottle.