In some fiction, the echoes are more than just a special effect -- they're literal. Other characters can see them and be confused by them, making them effective covers for highly elaborate martial arts attacks. In video games, they can be used as an excuse to force the player to use timing to hit the "real" image. For various reasons, using Speed Echoes for the Doppelganger Spin doesn't really make a whole heck of a lot of sense, but eh, roll with it. Examples of Speed Echoes include: