Motion blur uses a previous picture to create intermediate pictures between 2 frames of a video. It was created to make panorama shot or sport content more precise, since any frames from a movie are blurry and can be stuttery if the camera or an object move to fast, and filming a football ball at 25/30 fps will be jiterry too. Interpolating something that is already blurry makes a better result. If you want to add motion blur to a video game you do it in engine, because you don't want to use it on your UI, you don't want your character to be blurry, you don't want ghosting, you don't want artifacts, you don't want input delay, all the things that the tv motion blur will do.