Yes, if there is fast movement in a scene, then there will be big changes between one frame and another, which will look unnatural. In cameras, since the frame is exposed for a set amount of time, this motion blurs in that frame (the object moves from one place to another during the exposure, and you get a blurred look). In the human perceptual system, the brain blends things together across a period of time (so much the same effect).
So for fast moving/changing things, a perfectly sharp, frozen image changing to another perfectly sharp, frozen image looks unpleasant. Motion blur resolves this, helping the frames blend from one into another and give more of a sense of continual movement rather than suddenly moving from one location to another. It's less of an issue at higher frame rates, as you have smaller movements between each frame (less time has passed, the object has moved less far), even so, some motion blur is still a good idea :)