Tiny Baetis mayflies are perhaps the most commonly encountered and imitated by anglers on all American trout streams due to their great abundance, widespread distribution, and trout-friendly emergence habits.
Several years ago, anchored up in the Gamelands on the West Branch of the Delaware, I watched folks in a driftboat downstream unsuccessfully casting to a fish. When they moved on I pulled anchor and slowly slipped my canoe downstream looking for the rise. Soon I had made several unsuccessful drifts over the same fish when I remembered Bob Clouser telling me to twitch my Green Drake imitation, that browns knew the big bug should be moving. I was certain that I was going to mess it up, producing drag that would leave me pulling anchor and moving on without ever seeing the fish rise again. But twitch I did and a beautiful brown, called from the depths by the struggling emerger, came up and drank in the fly. It was absolute magic.
I agree that an animated move to a dry fly at certain times will get results when nothing else will. It is really cool to get that kind of feedback from wary fish. To screw with a normally deadly drag free drift takes SAND!