Zero drag float = Natural

In fly fishing for example you want your fly to float down the river with the current, neither faster nor slower and definitely not sideway. Heavily fished resident trout are notorious for ignoring anything unnatural. But there are always exceptions to the rule such as a drowning hopper trying to rescue itself. That is why you sometimes twitch your fly across the current. Same idea with any other lure (Bait, corkie, jig, wet fly, etc). The general idea is to have it flow with the current without it being too obviously slower or faster than current. But as I said earlier there is always exception. For example a lot of time fish hit at the end of your swing when your lure is going side way and up. This is not a natural flow but it has more to do with enhanced visibility (the object is going across the fish field of vision) and the chase instinct (The object is rising and getting away from the fish).