I tend to use this approach. It helps keep the collision area constant and easier to manage because you deal with one frame whereas if you relied on the collision poly of the animations, there is more chance you might set them wrong if you have many animations/frames, and you might also want to adjust various things about the sprite like widht/height rotation/angle, etc.. Those affect the collision poly and you may want to change them without affecting the collision box so a separate sprite for it is a way to keep things more manageable.
As for there being any delay with positioning to the collision box, you would need to position the sprite to the box after any box movement/positioning is done. If you position the sprite before any movement to the box is made, then there will be a noticeable delay.